Imaging device and image acquisition device

ABSTRACT

An imaging device includes a pixel comprising a photoelectric conversion layer having a first surface and a second surface opposite to the first surface; a pixel electrode on the first surface; an auxiliary electrode on the first surface, the auxiliary electrode being spaced from the pixel electrode; an upper electrode on the second surface, the upper electrode facing the pixel electrode and the auxiliary electrode; and an amplification transistor having a gate coupled to the pixel electrode. The imaging device also includes voltage application circuitry that generates a first voltage and a second voltage different from the first voltage, the voltage application circuitry being coupled to the auxiliary electrode. The voltage application circuitry selectively supplies either the first voltage or the second voltage to the auxiliary electrode.

CROSS REFERENCE

This application is a Continuation Application of U.S. application Ser.No. 14/876,500 filed Oct. 6, 2015, now allowed, which claims the benefitof Japanese Application No. 2015-123725 filed Jun. 19, 2015 and2014-216209 filed Oct. 23, 2014, the entire contents of each are herebyincorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to an imaging device and an imageacquisition device.

2. Description of the Related Art

As a metal oxide semiconductor (MOS) type imaging device, astacked-layer type imaging device has been proposed. In thestacked-layer type imaging device, a photoelectric conversion film isstacked on the outermost surface of a semiconductor substrate. Chargesgenerated by photoelectric conversion in the photoelectric conversionfilm are stored in a charge storage region. The imaging device reads thestored charges using a charge coupled device (CCD) circuit or acomplementary MOS (CMOS) circuit in the semiconductor substrate. Forinstance, Japanese Unexamined Patent Application Publication No.2009-164604 discloses such an imaging device.

SUMMARY

The imaging device is used in various environments. For instance, for animaging device for monitoring or mounting in a vehicle, capability ofpicking up an image of high quality even in an environment in whichbrightness changes significantly is demanded. Therefore, forconventional stacked-layer type imaging devices, capability of changingthe sensitivity has been demanded.

In one general aspect, an imaging device has a pixel including aphotoelectric conversion layer having a first surface and a secondsurface opposite to the first surface; a pixel electrode on the firstsurface; an auxiliary electrode on the first surface, the auxiliaryelectrode being spaced from the pixel electrode; an upper electrode onthe second surface, the upper electrode facing the pixel electrode andthe auxiliary electrode; and an amplification transistor having a gatecoupled to the pixel electrode. The imaging device also includes voltageapplication circuitry that generates a first voltage and a secondvoltage different from the first voltage, the voltage applicationcircuitry being coupled to the auxiliary electrode. The voltageapplication circuitry may selectively supply either the first voltage orthe second voltage to the auxiliary electrode.

It should be noted that general or specific embodiments may beimplemented as an element, a device, a system, an integrated circuit,and a method, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an example of a circuitconfiguration of an imaging device according to a first embodiment;

FIG. 2 is a schematic sectional view illustrating a typical example of aunit pixel cell in the imaging device according to the first embodiment;

FIG. 3 is a schematic plan view illustrating an example of a shape of apixel electrode and an auxiliary electrode;

FIG. 4A is a schematic sectional view illustrating an example of aregion for trapping charges which is formed in a photoelectricconversion layer when a sensitivity adjustment voltage is applied to theauxiliary electrode;

FIG. 4B is a schematic plan view illustrating an example of a region fortrapping charges which is formed in the photoelectric conversion layerwhen a sensitivity adjustment voltage is applied to the auxiliaryelectrode;

FIG. 4C is a schematic sectional view illustrating another example of aregion for trapping charges which is formed in the photoelectricconversion layer when a sensitivity adjustment voltage is applied to theauxiliary electrode;

FIG. 4D is a schematic plan view illustrating another example of aregion for trapping charges which is formed in the photoelectricconversion layer when a sensitivity adjustment voltage is applied to theauxiliary electrode;

FIG. 5 is a schematic diagram illustrating an exemplary relationshipbetween sensitivity adjustment voltage and sensitivity;

FIG. 6A is a schematic plan view illustrating an example of a region fortrapping charges which is formed in the photoelectric conversion layerwhen a first sensitivity adjustment voltage is applied to the auxiliaryelectrode together with an example of a region for trapping chargeswhich is formed in a photoelectric conversion layer when a secondsensitivity adjustment voltage is applied to the auxiliary electrode;

FIG. 6B is a schematic plan view illustrating another example of aregion for trapping charges which is formed in the photoelectricconversion layer when the first sensitivity adjustment voltage isapplied to the auxiliary electrode together with another example of aregion for trapping charges which is formed in a photoelectricconversion layer when the second sensitivity adjustment voltage isapplied to the auxiliary electrode;

FIG. 6C is a schematic plan view illustrating an example of a region fortrapping charges which is formed in the photoelectric conversion layerwhen the first sensitivity adjustment voltage lower than 0 is applied tothe auxiliary electrode;

FIG. 6D is a schematic plan view illustrating an example of a region fortrapping charges which is formed in the photoelectric conversion layerwhen the first sensitivity adjustment voltage is applied to theauxiliary electrode together with an example of a region for trappingcharges which is formed in the photoelectric conversion layer when thesecond sensitivity adjustment voltage is applied to the auxiliaryelectrode;

FIG. 7 is a timing chart illustrating an example of timing of change ina sensitivity adjustment voltage and in a reset gate voltage of theimaging device according to the first embodiment;

FIG. 8 is a timing chart illustrating another example of timing ofchange in the sensitivity adjustment voltage and in the reset gatevoltage of the imaging device according to the first embodiment;

FIG. 9 is a timing chart illustrating still another example of timing ofchange in the sensitivity adjustment voltage and in the reset gatevoltage of the imaging device according to the first embodiment;

FIG. 10 is a graph for explaining an example of operation in an imagingdevice having a flash;

FIG. 11 is a timing chart illustrating an example of timing of change inthe sensitivity adjustment voltage, in the voltage of an upperelectrode, and in the reset gate voltage of the imaging device accordingto the first embodiment;

FIG. 12A is a schematic diagram illustrating an example of planarstructure of a pixel electrode and an auxiliary electrode in an imagingdevice according to a second embodiment;

FIG. 12B is a timing chart illustrating an example of timing of changein a sensitivity adjustment voltage and in a reset gate voltage of theimaging device according to the second embodiment;

FIG. 12C is a timing chart illustrating another example of timing ofchange in the sensitivity adjustment voltage and in the reset gatevoltage of the imaging device according to the second embodiment;

FIG. 13A is a schematic diagram illustrating another example of planarstructure of the pixel electrode and the auxiliary electrode in theimaging device according to the second embodiment;

FIG. 13B is a timing chart illustrating still another example of timingof change in the sensitivity adjustment voltage and in the reset gatevoltage of the imaging device according to the second embodiment;

FIG. 14A is a schematic diagram illustrating an example of a circuitconfiguration of an imaging device according to a third embodiment;

FIG. 14B is a schematic diagram illustrating another example of aconfiguration of the imaging device according to the third embodiment;

FIG. 15 is a schematic diagram illustrating still another example of aconfiguration of the imaging device according to the third embodiment;

FIG. 16 is a plan view illustrating an example of disposition of pixelelectrodes and auxiliary electrodes in an imaging device having an inputinterface;

FIG. 17 is a schematic diagram illustrating an example of a circuitconfiguration of an imaging device according to a fourth embodiment;

FIG. 18 is a plan view illustrating an example of disposition of pixelelectrodes and auxiliary electrodes in the imaging device according tothe fourth embodiment;

FIG. 19 is a plan view illustrating another example of disposition ofthe pixel electrodes and the auxiliary electrodes in the imaging deviceaccording to the fourth embodiment;

FIG. 20 is a schematic diagram illustrating an example of electricalconnection between a voltage application circuit and a unit pixel cellincluding a pixel electrode and an auxiliary electrode;

FIG. 21 is a schematic cross-sectional view illustrating an example ofthe unit pixel cell including the pixel electrode and the auxiliaryelectrode;

FIG. 22 is a schematic diagram illustrating an example of a circuitconfiguration of an imaging device according to a fifth embodiment;

FIG. 23 is a plan view illustrating an example of disposition of pixelelectrodes and auxiliary electrodes in an imaging device according to asixth embodiment;

FIG. 24A is a schematic sectional view illustrating an example of aregion for trapping charges which is formed in a photoelectricconversion layer of the unit pixel cell;

FIG. 24B is a schematic sectional view illustrating an example of theregion for trapping charges in a state where a second sensitivityadjustment voltage is applied to a sub auxiliary electrode and a firstsensitivity adjustment voltage is applied to another sub auxiliaryelectrode;

FIG. 25A is a block diagram illustrating an example of a configurationof an image acquisition device according to a seventh embodiment;

FIG. 25B is a schematic diagram illustrating an example of aconfiguration of an illumination system in the image acquisition deviceaccording to the seventh embodiment;

FIG. 26A is an illustration for explaining an exemplary step forobtaining an image by the image acquisition device when a sensitivityadjustment voltage is applied to the auxiliary electrode;

FIG. 26B is an illustration for explaining an exemplary step forobtaining an image by the image acquisition device when the sensitivityadjustment voltage is applied to the auxiliary electrode;

FIG. 27 is a schematic diagram illustrating an example of pixelarrangement of a plurality of picked up images when the sensitivityadjustment voltage is applied to the auxiliary electrode;

FIG. 28A is a schematic diagram illustrating an example of relationshipbetween an incident light through an object to the region for trappingcharges and a direction of illumination when a sensitivity adjustmentvoltage is applied to the auxiliary electrode;

FIG. 28B is a schematic diagram illustrating another example ofrelationship between an incident light through an object to the regionfor trapping charges and a direction of illumination when a sensitivityadjustment voltage is applied to the auxiliary electrode;

FIG. 28C is a schematic diagram illustrating still another example ofrelationship between an incident light through an object to the regionfor trapping charges and a direction of illumination when a sensitivityadjustment voltage is applied to the auxiliary electrode;

FIG. 29 is a schematic diagram illustrating an example of pixelarrangement of a plurality of picked up images when the sensitivityadjustment voltage is applied to the auxiliary electrode; and

FIG. 30 is a schematic diagram illustrating another example of aconfiguration of an illumination system in the image acquisition deviceaccording to the seventh embodiment.

DETAILED DESCRIPTION

The embodiments according to the present disclosure will be describedwith reference to the drawings. In the following embodiments, an examplewill be described in which when a pair of a hole and an electron isgenerated by photoelectric conversion, the hole is detected as a signalcharge. An electron may serve as the signal charge. It is to be notedthat the present disclosure is not limited to the following embodiments.In addition, modifications may be made in a range without departing fromthe scope of the present disclosure in which the effect is achieved.Furthermore, one embodiment and another embodiment may also be combined.In the following description, the same or similar components are denotedby the same reference character. Also, redundant description may beomitted.

First Embodiment

An imaging device according to the present embodiment will be describedwith reference to FIGS. 1 to 11.

Structure of Imaging Device 101

FIG. 1 illustrates an example of a circuit configuration of an imagingdevice 101 according to a first embodiment. The imaging device 101includes a plurality of unit pixel cells 14 and a peripheral circuit.

The unit pixel cells 14 arranged two-dimensionally, that is, in the rowdirection and in the column direction on a semiconductor substrate toform a photosensitive area (pixel area). The imaging device 101 may be aline sensor, and the unit pixel cells 14 may be arrangedone-dimensionally. In the description of the present application, therow direction and the column direction indicate the directions in whichthe row and the column extend, respectively. That is, the columndirection is the vertical direction and the row direction is thehorizontal direction.

Each of the unit pixel cells 14 includes a photoelectric converter 10,an amplification transistor 11, a reset transistor 12, and an addresstransistor (row selection transistor) 13. As described in detail in thefollowing, in the present embodiment, the photoelectric converter 10includes a pixel electrode 50 and an auxiliary electrode 61. The amountof signal charge which is generated by photoelectric conversion andtrapped in the pixel electrode 50 is adjusted by adjusting a voltageapplied to the auxiliary electrode 61. That is, the sensitivity of theimaging device 101 is adjusted.

The imaging device 101 has a voltage application circuit 60. The voltageapplication circuit 60 is configured to be able to apply at least twomutually different voltages simultaneously or selectively to theauxiliary electrode 61 when the imaging device 101 is in operation. Itis sufficient that the voltage application circuit 60 have aconfiguration that allows a voltage supplied to the auxiliary electrode61 to be changed. The circuit configuration of the voltage applicationcircuit 60 is not limited to a specific circuit configuration. Forinstance, the voltage application circuit 60 may have a configuration inwhich a voltage supplied from a voltage source (not illustrated) isconverted to a predetermined voltage. Alternatively, the voltageapplication circuit 60 itself may be configured to generate apredetermined voltage. Hereinafter, the voltage supplied from thevoltage application circuit 60 to the auxiliary electrode 61 is referredto as a sensitivity adjustment voltage. The voltage application circuit60 supplies a sensitivity adjustment voltage to the auxiliary electrode61 via a sensitivity adjustment line 28, the sensitivity adjustmentvoltage according to a command from an operator who operates the imagingdevice 101 or a command from another control circuit provided in theimaging device 101. The voltage application circuit 60 is typicallyprovided as part of the peripheral circuit outside the photosensitivearea.

The pixel electrode 50 is connected to the gate electrode of theamplification transistor 11. The signal charge collected by the pixelelectrode 50 is stored in a charge storage node 24 located between thepixel electrode 50 and the gate electrode of the amplificationtransistor 11. Although a hole serves as a signal charge in the presentembodiment, an electron may serve as the signal charge.

The signal charge stored in the charge storage node 24 is applied to thegate electrode of the amplification transistor 11 as a voltage accordingto the amount of the signal charge. The amplification transistor 11amplifies the voltage. The signal voltage is selectively read by theaddress transistor 13. The source or drain electrode of the resettransistor 12 is connected to the pixel electrode 50. The resettransistor 12 resets the signal charge which is stored in the chargestorage node 24. In other words, the reset transistor 12 resets thepotentials of the gate electrode of the amplification transistor 11 andthe pixel electrode 50.

In order to selectively perform the above-described operations in eachof the unit pixel cells 14, the imaging device 101 includes a powersupply line 21, a vertical signal line 17, an address signal line 26 anda reset signal line 27. These lines are each connected to the unit pixelcells 14. The power supply line 21 is connected to the source or drainelectrode of the amplification transistor 11. The vertical signal line17 is connected to the source or drain electrode of the addresstransistor 13. The address signal line 26 is connected to the gateelectrode of the address transistor 13. Also, the reset signal line 27is connected to the gate electrode of the reset transistor 12.

The imaging device 101 includes a photoelectric converter control line16 for applying a predetermined voltage to the photoelectric converter10. The voltage supplied to the photoelectric converter 10 via thephotoelectric converter control line 16 may be used in common among allthe photoelectric converters 10. The voltage supplied to thephotoelectric converter 10 via photoelectric converter control line 16may be a nearly constant magnitude or a time varying voltage asdescribed later.

In the configuration illustrated to FIG. 1, the peripheral circuitincludes a vertical scanning circuit 15, a horizontal signal readcircuit 20, a plurality of column signal processing circuits 19, aplurality of load circuits 18, and a plurality of inverting amplifiers22. The vertical scanning circuit 15 is also called a row scanningcircuit. The horizontal signal read circuit 20 is also called a columnscanning circuit. The column signal processing circuits 19 are each alsocalled a row signal storage circuit. The inverting amplifiers 22 areeach also called a feedback amplifier.

The vertical scanning circuit 15 is connected to the address signal line26 and the reset signal line 27. The vertical scanning circuit 15selects the unit pixel cells 14 disposed in each row at a time, andreads a signal voltage and resets the potential of the pixel electrode50. The power supply line (source follower power supply) 21 supplies apredetermined power supply voltage to each of the unit pixel cells 14.The horizontal signal read circuit 20 is electrically connected to thecolumn signal processing circuits 19. The column signal processingcircuits 19 are electrically connected to the unit pixel cells 14disposed in each of the columns via a vertical signal line 17corresponding to the column. Each of the load circuits 18 iselectrically connected to a corresponding vertical signal line 17. Theload circuit 18 and the amplification transistor 11 form a sourcefollower circuit.

Each column is provided with a corresponding one of the invertingamplifiers 22. The input terminal of the negative side of the invertingamplifier 22 is connected to a corresponding vertical signal line 17.Also, the output terminal of the inverting amplifier 22 is connected tothe unit pixel cells 14 in a corresponding column via a feedback line 23corresponding to the column.

The vertical scanning circuit 15 applies a row selection signal to thegate electrode of the address transistor 13 via the address signal line26, the row selection signal controlling ON and OFF of the addresstransistor 13. In this manner, the rows to be read are scanned andselected. A signal voltage is read from the unit pixel cells 14 in theselected row to the vertical signal line 17. In addition, the verticalscanning circuit 15 applies a reset signal to the gate electrode of thereset transistor 12 via the reset signal line 27, the reset signalcontrolling ON and OFF of the reset transistor 12. In this manner, therow of target unit pixel cells 14 to be reset is selected. The verticalsignal line 17 transmits signal voltages read from the unit pixel cells14 selected by the vertical scanning circuit 15 to the column signalprocessing circuits 19.

The column signal processing circuits 19 each perform noise oppressionsignal processing represented by, for instance, correlation doublesampling, and analog-to-digital conversion (A/D conversion).

The horizontal signal read circuit 20 successively reads signals fromthe column signal processing circuits 19 and outputs signals to ahorizontal common signal line 29.

The inverting amplifier 22 is connected to the drain electrodes of thecorresponding reset transistor 12 via a feedback line 23. Therefore,when the address transistor 13 and the reset transistor 12 are in aconductive state, the inverting amplifier 22 receives an output of theaddress transistor 13 at a negative terminal. The inverting amplifier 22performs a feedback operation so that the gate potential of theamplification transistor 11 reaches a predetermined feedback voltage. Inthis operation, the value of an output voltage of the invertingamplifier 22 is 0 V or a positive voltage close to 0 V. The feedbackvoltage indicates the output voltage of the inverting amplifier 22.

Device Structure of Unit Pixel Cell 14

FIG. 2 schematically illustrates a cross-section of the device structureof a unit pixel cell 14 in the imaging device 101 according to thepresent embodiment.

The unit pixel cell 14 includes a semiconductor substrate 31, a chargedetection circuit 25, and a photoelectric converter 10. Thesemiconductor substrate 31 is, for instance, p-type silicon substrate.The charge detection circuit 25 detects signal charge trapped in thepixel electrode 50 and outputs a signal voltage. The charge detectioncircuit 25 includes the amplification transistor 11, the resettransistor 12, and the address transistor 13, and is formed in thesemiconductor substrate 31.

The amplification transistor 11 is formed in the semiconductor substrate31, and includes n-type impurity regions 41C and 41D that serve as adrain and a source, respectively, a gate insulating layer 38B located onthe semiconductor substrate 31, and a gate electrode 39B located on thegate insulating layer 38B.

The reset transistor 12 is formed in the semiconductor substrate 31, andincludes n-type impurity regions 41B and 41A that serve as a drain and asource, respectively, a gate insulating layer 38A located on thesemiconductor substrate 31, and a gate electrode 39A located on the gateinsulating layer 38A.

The address transistor 13 is formed in the semiconductor substrate 31,and includes n-type impurity regions 41D and 41E that serve as a drainand a source, respectively, a gate insulating layer 38C located on thesemiconductor substrate 31, and a gate electrode 39C located on the gateinsulating layer 38C. The n-type impurity region 41D is shared by theamplification transistor 11 and the address transistor 13, and therebythe amplification transistor 11 and the address transistor 13 areconnected in series.

In the semiconductor substrate 31, an element separation region 42 isprovided between adjacent unit pixel cells 14 and between theamplification transistor 11 and the reset transistor 12. The elementseparation region 42 achieves electrical separation between the adjacentunit pixel cells 14. Also, leakage of the signal charge stored in thecharge storage node is avoided.

Interlayer insulating layers 43A, 43B, and 43C are stacked on thesurface of the semiconductor substrate 31. In the interlayer insulatinglayer 43A, there are provided a contact plug 45A connected to the n-typeimpurity region 41B of the reset transistor 12, a contact plug 45Bconnected to the gate electrode 39B of the amplification transistor 11,and a wired line 46A that connects the contact plug 45A and the contactplug 45B. Thus, the n-type impurity region 41B (drain) of the resettransistor 12 is electrically connected to the gate electrode 39B of theamplification transistor 11.

The photoelectric converter 10 is provided on the interlayer insulatinglayer 43C. The photoelectric converter 10 includes an upper electrode52, a photoelectric conversion layer 51, the pixel electrode 50, and theauxiliary electrode 61. The photoelectric conversion layer 51 isinterposed between the upper electrode 52 and the pixel electrode 50,the auxiliary electrode 61. The pixel electrode 50 and the auxiliaryelectrode 61 are provided on the interlayer insulating layer 43C. Theupper electrode 52 is composed of, for instance, a conductivetransparent material such as ITO. The pixel electrode 50 and theauxiliary electrode 61 are composed of, for instance, metal includingaluminum or copper, or polysilicon which is doped with impurities to beconductive.

Although not illustrated in FIG. 2, the unit pixel cell 14 may have amicro lens on the upper electrode 52 of the photoelectric converter 10.Alternatively, the unit pixel cell 14 may have a color filter.

FIG. 3 illustrates an example of a shape of the pixel electrode 50 andthe auxiliary electrode 61 on the surface of the interlayer insulatinglayer 43C. FIG. 3 illustrates nine unit pixel cells that are arranged ina matrix with 3 rows and 3 columns. The pixel electrode 50 has aquadrilateral shape, for instance. In the present embodiment, asillustrated in FIG. 3, the pixel electrode 50 has a rectangular shapeand the auxiliary electrode 61 has a ring-shaped rectangular shape thatsurrounds the pixel electrode 50. The pixel electrode 50 and theauxiliary electrode 61 are spaced apart by distance L1. In thisinstance, the respective auxiliary electrodes 61 are formed integrallybetween nine unit pixel cells 14 illustrated are electrically connectedto one another.

Although the pixel electrode 50 is rectangular in the presentembodiment, the pixel electrode 50 may have a circular shape or apolygonal shape having five sides or more. Although the auxiliaryelectrode 61 surrounds the pixel electrode 50 in the present embodiment,the auxiliary electrode 61 may not surround the pixel electrode 50.

As illustrated in FIG. 2, the pixel electrode 50 is connected to thewired line 46A via a plug 47C provided in the interlayer insulatinglayer 43C, a wired line 46C provided on the interlayer insulating layer43B, a plug 47B provided in the interlayer insulating layer 43B, a wiredline 46B provided on the interlayer insulating layer 43A, and a plug 47Aprovided in the interlayer insulating layer 43A. Also, the auxiliaryelectrode 61 is connected to a wired line 49 provided on the interlayerinsulating layer 43B via a plug 48 provided in the interlayer insulatinglayer 43C. These plugs, contact plugs, and wired lines are composed ofmetal such as aluminum or copper, or polysilicon which is doped withimpurities to be conductive.

In the present embodiment, the imaging device 101 detects signal charge,that is, holes among the electron-hole pairs generated by photoelectricconversion in the photoelectric conversion layer 51. The signal chargeto be detected is stored in the above-described charge storage node 24(see FIG. 1). The charge storage node 24 includes the pixel electrode50, the gate electrode 39B, the n-type impurity region 41B, and theplugs 47A, 47B, 47C, the contact plugs 45A, 45B, and the wired lines46C, 46B, 46A (see FIG. 2) that connect those electrodes and region.

The photoelectric conversion layer 51 covers the auxiliary electrode 61and the pixel electrode 50 on the interlayer insulating layer 43C and isformed continuously over the entire portion of the unit pixel cells 14.The photoelectric conversion layer 51 is composed of, for instance, anorganic material or an amorphous silicon.

Although not illustrated in FIG. 2, the peripheral circuits (here thevertical scanning circuit 15, the horizontal signal read circuit 20, thecolumn signal processing circuit 19, load circuit 18, and the invertingamplifier 22) are also formed in the semiconductor substrate 31.

The imaging device 101 may be manufactured using a general semiconductormanufacturing process. In particular, when a silicon substrate is usedas the semiconductor substrate 31, the imaging device 101 may bemanufactured by utilizing various silicon semiconductor processes.

Operation of Imaging Device 101

Next, the exemplary operation of the imaging device 101 will bedescribed with reference to FIG. 1, FIG. 2, and FIGS. 4A to 4D. Asdescribed below, when a hole is used as a signal charge, the potentialof the pixel electrode 50 and the auxiliary electrode 61 is set lowerthan the potential of the upper electrode 52, thereby making it possibleto collect the holes generated in photoelectric conversion near thepixel electrode 50.

First, a voltage of approximately 10 V is applied to the upper electrode52. Furthermore, the reset transistor 12 is turned ON, and subsequentlyis turned OFF, thereby resetting the potential of the pixel electrode50. By the resetting, the potential of the charge storage node 24including the pixel electrode 50 is set to a reset voltage (forinstance, 0 V) as an initial value. Also, a first sensitivity adjustmentvoltage lower than the reset voltage (here, 0 V) for instance, isapplied to the auxiliary electrode 61 from the voltage applicationcircuit 60. Here, a voltage of −2 V is applied to the auxiliaryelectrode 61 as the first sensitivity adjustment voltage.

Like this, the potential of the pixel electrode 50 and the auxiliaryelectrode 61 is set lower than that of the upper electrode 52.Therefore, holes generated by photoelectric conversion in thephotoelectric conversion layer 51 move to the auxiliary electrode 61 andthe pixel electrode 50. Here, the potential of the auxiliary electrode61 is lower than the potential of the pixel electrode 50. That is, thepotential difference between the auxiliary electrode 61 and the upperelectrode 52 is higher than the potential difference between the pixelelectrode 50 and the upper electrode 52. Therefore, generated holes aremore likely to move to the auxiliary electrode 61 than to the pixelelectrode 50. Consequently, holes generated in region 51A (see FIG. 4A)including the overlapping portion with the pixel electrode 50 in a planview within the photoelectric conversion layer 51, mainly move to thepixel electrode 50 and are detected as signal charge. On the other hand,holes generated in region 51B (see FIG. 4A) including the overlappingportion with the auxiliary electrode 61 in a plan view within thephotoelectric conversion layer 51, mainly move to the auxiliaryelectrode 61. This indicates that among the light emitted to thephotoelectric conversion layer 51, the light emitted to the region 51Ais detected. That is, the unit pixel cell 14 substantially detects thelight incident to the region 51A among the light incident to the pixelregion. The region 51A is such a region that signal charge (here, holes)generated by photoelectric conversion in the region of the photoelectricconversion layer 51 mainly move to the pixel electrode. The region 51Bis such a region that signal charge (here, holes) generated byphotoelectric conversion in the region of the photoelectric conversionlayer 51 mainly move to the auxiliary electrode.

FIG. 4B is a plan view of the region 51A seen from a side of the pixelelectrode 50 and auxiliary electrode 61. In this example, the region 51Ahas a first area slightly greater than the pixel electrode 50, in aplane parallel to the photoelectric conversion layer 51. As illustratedin FIG. 4B, the shape and area of the region 51A as seen in a directionnormal to the surface of the semiconductor substrate 31 does notnecessarily match with the shape and area of the pixel electrode 50. Inaddition, as described in detail below, the shape and/or area of theregion 51A may vary with a voltage applied to the pixel electrode 50,the auxiliary electrode 61, and the upper electrode 52. The shape andarea of the region 51B as seen in a direction normal to the surface ofthe semiconductor substrate 31 also does not necessarily match with theshape and area of the auxiliary electrode 61. FIG. 4A and FIG. 4B merelyschematically illustrate the region 51A and no clear boundary existsbetween the region 51A and the region 51B.

Signal charge is stored for each of frames and the stored charge and thepotential of the pixel electrode 50 are reset with the first sensitivityadjustment voltage applied to the auxiliary electrode 61. In thismanner, it is possible to detect charge generated in the region 51Ahaving the first area from among the charge which is generated byphotoelectric conversion in the photoelectric conversion layer 51.

FIG. 4C and FIG. 4D illustrate an example in which the voltageapplication circuit 60 applies a second sensitivity adjustment voltagehigher than the first sensitivity adjustment voltage to the auxiliaryelectrode 61. For instance, the second sensitivity adjustment voltage is5 V.

Similarly to the case where the first sensitivity adjustment voltage isapplied, also in this example, the holes generated by photoelectricconversion in the photoelectric conversion layer 51 move to theauxiliary electrode 61 and the pixel electrode 50. In this example, thesecond sensitivity adjustment voltage (here, 5 V) is higher than thereset voltage (here, 0 V). Therefore, the holes generated in thephotoelectric conversion layer 51 are more likely to move to the pixelelectrode 50 than to the auxiliary electrode 61.

Furthermore, in this example, the second sensitivity adjustment voltage,which is higher than the first sensitivity adjustment voltage in theexample described with reference to FIG. 4A and FIG. 4B, is applied tothe auxiliary electrode 61. Therefore, the amount of holes that flowinto the auxiliary electrode 61 is smaller than in the case where thefirst sensitivity adjustment voltage is applied to the auxiliaryelectrode 61. That is, the generated holes are much more likely to moveto the pixel electrode 50. Consequently, as schematically illustrated inFIG. 4C, region 51C, in which holes movable to the pixel electrode 50are distributed, is larger than the region 51A (see FIG. 4A) in the casewhere the first sensitivity adjustment voltage is applied to theauxiliary electrode 61. In addition, region 51D, in which holes movableto the auxiliary electrode 61 are distributed, is smaller than theregion 51B (see FIG. 4A) in the case where the first sensitivityadjustment voltage is applied to the auxiliary electrode 61.

FIG. 4D is a plan view of the region 51C seen from a side of the pixelelectrode 50 and auxiliary electrode 61. The region 51C has a secondarea larger than the first area, in a plane parallel to thephotoelectric conversion layer 51.

Signal charge is stored for each of frames and the stored charge and thepotential of the pixel electrode 50 are reset with the secondsensitivity adjustment voltage applied to the auxiliary electrode 61. Inthis manner, it is possible to detect charge generated in the region 51Chaving the second area from among the charge which is generated byphotoelectric conversion in the photoelectric conversion layer 51.

When the first sensitivity adjustment voltage is applied to theauxiliary electrode 61 in this manner, the region 51A where signalcharges are trapped by the pixel electrode 50 is relatively small. Whenthe second sensitivity adjustment voltage is applied, the region 51Cwhere signal charges are trapped by the pixel electrode 50 is relativelylarge. That is, when the first sensitivity adjustment voltage is appliedto the auxiliary electrode 61, the sensitivity of the imaging device 101is relatively low. When the second sensitivity adjustment voltage isapplied, the sensitivity is relatively high. In this manner, thesensitivity of the imaging device 101 is changeable by changing thesensitivity adjustment voltage applied to the auxiliary electrode 61. Asthe distance L1 (see FIG. 4A and FIG. 4C) between the pixel electrode 50and the auxiliary electrode 61 increases, the size of the region (here,regions 51A, 51C) where signal charges are trapped by the pixelelectrode 50 is adjustable in a wider range by changing the sensitivityadjustment voltage.

FIG. 5 schematically illustrates the relationship between thesensitivity adjustment voltage applied to the auxiliary electrode andthe sensitivity of the imaging device 101 when a hole serves as a signalcharge. As illustrated in FIG. 5, when the sensitivity adjustmentvoltage applied to the auxiliary electrode is changed, the sensitivityalso changes. For instance, when the sensitivity adjustment voltage isincreased the sensitivity increases. Like this, according to the presentembodiment, the imaging device having a variable sensitivity isachieved.

Although a hole serves as a signal charge in the above-describedembodiment, an electron may be used as a signal charge. When an electronserves as a signal charge, a voltage higher than the potential of theupper electrode 52 is applied to the pixel electrode 50 and theauxiliary electrode 61. Thus, electrons generated by photoelectricconversion move to the pixel electrode 50 and the auxiliary electrode61. When an electron serves as a signal charge, electrons are morelikely to flow to the pixel electrode and the sensitivity of the imagingdevice increases with a relatively lower sensitivity adjustment voltageapplied to the auxiliary electrode. On the other hand, electrons aremore likely to flow to the auxiliary electrode and the sensitivity ofthe imaging device decreases with a relatively higher sensitivityadjustment voltage applied to the auxiliary electrode.

Like this, it is possible to change the sensitivity of the imagingdevice 101 by switching the sensitivity adjustment voltage applied tothe auxiliary electrode 61 from the voltage application circuit 60. Inthe case where a hole is used as a signal charge, when the potentialdifference between the upper electrode 52 and the auxiliary electrode 61is greater than the potential difference between the upper electrode 52and the pixel electrode 50, the sensitivity of the imaging devicebecomes relatively low. On the other hand, when the potential differencebetween the upper electrode 52 and the auxiliary electrode 61 is lessthan the potential difference between the upper electrode 52 and thepixel electrode 50, the sensitivity of the imaging device becomesrelatively high. It is to be noted that this relationship holds in thecase where an electron is used as a signal charge.

In the aforementioned example described with reference to FIGS. 4A to4D, the sensitivity adjustment voltage applied to the auxiliaryelectrode 61 is changed between a value higher and a value lower thanthe reset voltage of the pixel electrode 50. However, even when thesensitivity adjustment voltage applied to the auxiliary electrode 61 ischanged in a range higher than or a range lower than the reset voltageof the pixel electrode 50, the sensitivity of the imaging device 101 ischangeable. For instance, in the case where a hole is used as a signalcharge and the sensitivity adjustment voltage is changed in a rangelower than the reset voltage of the pixel electrode 50, the sensitivityof the imaging device is decreased as the potential difference betweenthe pixel electrode 50 and the auxiliary electrode 61 is relativelyincreased.

Next, the value of sensitivity adjustment voltage applied to theauxiliary electrode 61 and the characteristics of the imaging device 101achieved by the sensitivity adjustment voltage will be further describedwith reference to FIGS. 6A to 6D.

First, let Vr be the reset voltage of the pixel electrode 50 and a casewill be described where a hole serves as a signal charge. FIG. 6A is aplan view of a region where signal charges are trapped by the pixelelectrode 50, the plan view seen from a side of the pixel electrode 50and the auxiliary electrode 61 when sensitivity adjustment voltages V1and V2 satisfying V1<Vr<V2 are applied to the auxiliary electrode 61. InFIG. 6A, regions 51A1, 51Ar, 51A2 schematically illustrate respectiveregions where signal charges (here, holes) are trapped by the pixelelectrode 50 when sensitivity adjustment voltages of V1, Vr, V2 areapplied to the auxiliary electrode 61. When the reset voltage Vr isapplied to the auxiliary electrode 61, initialized pixel electrode 50and auxiliary electrode 61 have the same potential. Therefore, when thereset voltage Vr is applied to the auxiliary electrode 61, the outerperiphery of the region 51Ar is located at approximately the midpointbetween the pixel electrode 50 and the auxiliary electrode 61.

When a hole serves as a signal charge, the lower the voltage applied tothe auxiliary electrode 61, it is more likely that holes serving assignal charges are trapped by the auxiliary electrode 61 and the regionwhere signal charges are trapped by the pixel electrode 50 is decreased.Therefore, the region 51A1 formed when the sensitivity adjustmentvoltage V1 lower than Vr is applied is smaller than the region 51Ar whenVr is applied. Also, the region 51A2 formed when the sensitivityadjustment voltage V2 higher than Vr is applied is larger than theregion 51Ar when Vr is applied. In this manner, the sensitivityadjustment voltage V1 lower than the reset voltage Vr and thesensitivity adjustment voltage V2 higher than the reset voltage Vr areselectively applied, thereby making it possible to greatly change thesize of region where holes are trapped by the pixel electrode 50. Thatis, the imaging device 101 having a wide adjustable range of sensitivitymay be achieved.

FIG. 6B is a plan view of a region where signal charges are trapped bythe pixel electrode 50, the plan view seen from a side of the pixelelectrode 50 and the auxiliary electrode 61 when sensitivity adjustmentvoltages V1 and V2 satisfying Vr<V1<V2 are applied to the auxiliaryelectrode 61. The region 51A1 formed when the sensitivity adjustmentvoltage V1 higher than Vr is applied is larger than the region 51Ar whenVr is applied. Also, the region 51A2 formed when the sensitivityadjustment voltage V2 higher than V1 is applied is further larger thanthe region 51A1 when V1 is applied. Therefore, by applying thesensitivity adjustment voltage V1 satisfying the relationship Vr<V1<V2to the auxiliary electrode 61, it is possible to ensure favorablesensitivity to some extent while suppressing color mixing between unitpixel cells. In addition, by applying the sensitivity adjustment voltageV2 to the auxiliary electrode 61, higher sensitivity may be achieved.

FIG. 6C is a plan view of a region where signal charges are trapped bythe pixel electrode 50, the plan view seen from a side of the pixelelectrode 50 and the auxiliary electrode 61 when sensitivity adjustmentvoltages V1 satisfying V1<Vr and V1<0 are applied to the auxiliaryelectrode 61. By setting the sensitivity adjustment voltage V1 to anegative value, a great number of holes are trapped by the auxiliaryelectrode 61, and thus the region 51A1 is decreased. Consequently, thesensitivity is decreased and an imaging device may be implemented inwhich an overexposed white area is not likely to occur even in a brightenvironment. It is to be noted that when a negative voltage is used as avoltage for driving (switching between ON and OFF of) the transistors(such as the reset transistor 12, the address transistor 13) provided ineach pixel, the negative voltage may also be used as the sensitivityadjustment voltage applied to the auxiliary electrode 61. For instance,when the reset transistor 12 is turned ON or OFF by applying a negativevoltage to the gate voltage of the reset transistor 12, a circuit forgenerating a gate voltage may be used as the voltage application circuit60. Thus, the size of the peripheral circuits may be reduced and/or theconfiguration of the peripheral circuits may be simplified. AlthoughFIG. 6C illustrates the case where V1<Vr and V1<0, the relationship maybe such that V1≥Vr and V1<0.

When an electron serves as a signal charge, it is sufficient to invertthe magnitude relationship between V1, V2, Vr as in the case where ahole serves as a signal charge. For instance, the sensitivity adjustmentvoltages V1 and V2 satisfying V1<V2<Vr may be applied to the auxiliaryelectrode 61. FIG. 6D is a plan view of a region where signal charges(here, electrons) are trapped by the pixel electrode 50, the plan viewseen from a side of the pixel electrode 50 and the auxiliary electrode61 when sensitivity adjustment voltages V1 and V2 satisfying V1<V2<Vrare applied to the auxiliary electrode 61. It is to be noted that anelectron is assumed to serve as a signal charge.

When an electron serves as a signal charge, the lower the voltageapplied to the auxiliary electrode 61 is, it is more unlikely thatsignal charges (here, electrons) are trapped by the auxiliary electrode61 and the region where signal charges are trapped by the pixelelectrode 50 increases. Therefore, the region 51A2 when the sensitivityadjustment voltage V2 lower than Vr is applied is larger than the region51Ar when Vr is applied. Also, the region 51A1 formed when thesensitivity adjustment voltage V1 further lower than V2 is applied maybe made further larger than the region 51A2 when V2 is applied.Therefore, by applying the sensitivity adjustment voltage V2 satisfyingthe relationship V1<V2<Vr to the auxiliary electrode 61, it is possibleto ensure favorable sensitivity to some extent while suppressing colormixing between unit pixel cells. In addition, by applying thesensitivity adjustment voltage V1 to the auxiliary electrode 61, highersensitivity may be achieved.

Next, an exemplary method of driving the imaging device 101 with thesensitivity adjustment voltage varied will be described with referenceto FIGS. 1 to 7. FIG. 7 is a timing chart illustrating an example oftiming of application of the sensitivity adjustment voltage and exposurein the imaging device 101.

In FIG. 7, RST1, RST2, . . . , RSTn indicate the timing of a gatevoltage (hereinafter may be referred to as a reset gate voltage) to beapplied to the gate electrodes of the reset transistors 12 included inthe 1st, 2nd, . . . , nth rows, respectively. As described withreference to FIG. 1, the imaging device 101 performs, for instance,exposure and reading of signals for each row. This is called a rollingshutter. The charge storage nodes 24 in the unit pixel cells 14 in eachrow are successively reset during the period of one frame by applicationof the reset gate voltage. The exposure time corresponds to the perioduntil the subsequent reset gate voltage is applied after the reset gatevoltage is applied to each row of the pixel array.

In the example indicated in FIG. 7, sensitivity adjustment voltage SSVapplied to the auxiliary electrode 61 is changed at the start of asecond frame. As described with reference to FIG. 3, in the presentembodiment, the auxiliary electrode 61 is continuously formed over theunit pixel cells 14. That is, in the configuration illustrated in FIG.3, the sensitivity adjustment voltage applied to the auxiliary electrode61 is controlled not row by row but as a whole at the same timing.Although the sensitivity adjustment voltage is controlled in the entirepixel array at the same timing, the timing of starting exposure isshifted for each row of the pixel array as seen from FIG. 7. Therefore,when the sensitivity adjustment voltage applied to the auxiliaryelectrode 61 is changed at any time, the sensitivity adjustment voltageis changed during the exposure time. In the frame (here, the secondframe) in which the sensitivity adjustment voltage is changed, thesensitivity is different for each row. Also, the sensitivity adjustmentvoltage is changed in the middle of the exposure time, and thus incidentlight is not detectable with proper sensitivity corresponding to theapplied sensitivity adjustment voltage. For this reason, the image datapicked up in the second frame, in which the sensitivity adjustmentvoltage is changed, is discarded. In the subsequent third frame, thesensitivity adjustment voltage after the variation has been applied toeach row since the start of exposure, and consequently, incident lightis detectable with proper sensitivity in all the rows.

Thus, when the sensitivity adjustment voltage applied to the auxiliaryelectrode 61 is changed per unit of at least two frames, an image withchanged sensitivity may be obtained per unit of frame. Thus, accordingto the present embodiment, the sensitivity of the imaging device may bechanged per unit of frame by changing the value of the sensitivityadjustment voltage which is supplied from the voltage applicationcircuit. Consequently, the imaging device that is capable of picking upan image of high quality in various environments in which brightnesschanges significantly is achieved.

In addition, the auxiliary electrodes 61 of the unit pixel cells 14 areconnected to one another and so the sensitivity adjustment voltage maybe applied to the auxiliary electrodes 61 at the same time, and therebywired lines for driving auxiliary electrodes may be reduced.

It is to be noted that Japanese Unexamined Patent ApplicationPublication No. 2008-112907 and International Publication No. WO2013/001809 disclose the use of a shield electrode for prevention ofcolor mixing. In this technique, it is preferable that the sensitivityadjustment voltage applied to the shield electrode be nearly constant inorder to obtain the technical effect. Therefore, the technique of thepresent disclosure, that is, sensitivity is adjusted by the sensitivityadjustment voltage applied to the auxiliary electrode is based oncompletely different ideas from the technique disclosed in the citedliterature.

Modification of First Embodiment

In the operation described with reference to FIG. 7, the sensitivityadjustment voltage applied to the auxiliary electrode 61 is changed perunit of two frames. However, switching of sensitivity adjustment voltageis not limited to per unit of two frames. As described below, switchingof sensitivity adjustment voltage may be performed per unit of oneframe.

FIG. 8 is a timing chart illustrating another example of timing ofapplication of the sensitivity adjustment voltage, exposure and signalreading. In the example illustrated in FIG. 8, the voltage applicationcircuit 60 switches the sensitivity adjustment voltage SSV from V0 to Vsin one frame. Furthermore, the voltage application circuit 60 switchesthe sensitivity adjustment voltage SSV to V0 after elapse of a certaintime.

In this example, the voltage V0 is sufficiently low voltage to make thesensitivity of the imaging device 101 nearly 0. That is, in a statewhere the voltage V0 is applied to the auxiliary electrode 61, mostsignal charges (here, electron holes) generated in the photoelectricconversion layer 51 are trapped by the auxiliary electrode 61. In otherwords, in a state where the voltage V0 is applied to the auxiliaryelectrode 61, the region (see the region 51A illustrated in FIG. 4A andFIG. 4B) where signal charges are trapped by the pixel electrode 50 issufficiently small, and only a slight amount of signal charges istrapped by the pixel electrode 50. That is, application of the voltageV0 to the auxiliary electrode 61 achieves a state that is as if aphotosensitive region is shielded from light. On the other hand,application of voltage Vs moderately higher than the voltage V0 to theauxiliary electrode 61 enables the region 51A to expand moderately wheresignal charges are trapped by the pixel electrode 50, and it is possibleto provide the imaging device 101 with the sensitivity necessary forimage pickup.

In the example illustrated in FIG. 8, the voltage Vs is applied to theauxiliary electrode 61 during a certain period in one frame and thevoltage V0 is applied to the auxiliary electrode 61 in other periods.Therefore, signal charges are collected by the pixel electrode 50 exceptfor the period in which the voltage V0 is applied to the auxiliaryelectrode 61 and the sensitivity becomes nearly 0. That is, the period,within a frame, during which the voltage Vs is applied to the auxiliaryelectrode 61 contributes to the storage of signal charges as effectiveexposure time.

Like this, according to the present embodiment, it is possible to adjusteffective exposure time by the period during which the voltage Vs isapplied to the auxiliary electrode 61. As illustrated in FIG. 8, theeffective exposure time may be in common between all the unit pixelcells 14. Therefore, it is possible to synchronize the exposure periodsin all the unit pixel cells included in the pixel array. That is, afunction similar to what is called global shutter may be achieved bychanging the sensitivity adjustment voltage in each frame withoutseparately providing a capacity element for storing signal charges ineach pixel.

FIG. 9 is a timing chart illustrating still another example of timing ofapplication of the sensitivity adjustment voltage, exposure and signalreading. As described with reference to FIG. 8, the sensitivity in theimaging device 101 may be decreased to nearly 0 by applying the voltageV0 with an appropriate magnitude to the auxiliary electrode 61. That is,it is possible to use the sensitivity adjustment voltage applied to theauxiliary electrode 61 instead of a shudder. Similarly to the exampledescribed with reference to FIG. 8, also in this example, signal chargesare stored in the period during which the voltage Vs is applied to theauxiliary electrode 61. The period during which the voltage V0 isapplied to the auxiliary electrode 61 does not effectively contribute toacquisition of an image.

In the example illustrated in FIG. 9, the voltage application circuit 60switches the sensitivity adjustment voltage SSV between V0 and Vsperiodically. Therefore, an effective exposure period and a non-exposureperiod are repeated periodically. For instance, when image pickup isperformed using a lighting fixture having periodic flickering, theeffect of the periodic flickering of the lighting fixture may becanceled by varying the voltage applied to the auxiliary electrode 61periodically.

FIG. 10 is a timing chart illustrating still another example of timingof application of the sensitivity adjustment voltage, exposure andsignal reading. FIG. 10 is a timing chart for explaining an example ofoperation in an imaging device having a flash (for instance, see FIG.14B described later). FIG. 10 illustrates the change in the sensitivityadjustment voltage SSV, the change in the reset gate voltage of each rowof the pixel array, and the timing of firing the flash.

In the example illustrated in FIG. 10, a flash operation is performed inthe second frame. The voltage application circuit 60 changes thesensitivity adjustment voltage SSV in synchronization with the flash.Specifically, the voltage application circuit 60 applies the voltage Vsto the auxiliary electrode 61 during the period in which the flash isoff, and, applies voltage Vt lower than the voltage Vs to the auxiliaryelectrode 61 during the period in which the flash is on. That is, theflash operation is performed so that the sensitivity of the imagingdevice is low during the period in which the flash is on.

In this manner, the sensitivity adjustment voltage SSV may be changed sothat the sensitivity of the imaging device is temporarily decreasedduring the period in which the flash is on. The temporary decrease inthe sensitivity of the imaging device during the period in which theflash is on may suppress occurrence of an overexposed white area. Inaddition, the effect of locus of light due to movement of a bright spotsuch as reflection of flash may be removed. Instead of the voltage Vt,the aforementioned voltage V0, which makes the sensitivity of theimaging device nearly 0, may be applied to the auxiliary electrode 61.

FIG. 11 is a timing chart illustrating still another example of timingof application of the sensitivity adjustment voltage, exposure andsignal reading. FIG. 11 illustrates the change in the sensitivityadjustment voltage SSV, the change in the reset gate voltage of each rowof the pixel array, and the change in the voltage applied to the upperelectrode 52. As described below, the magnitude of a voltage applied tothe upper electrode 52 may be changed according to the change in thesensitivity adjustment voltage SSV.

Here, similarly to the example described with reference to FIG. 8, theperiod in which the voltage V0 is applied to the auxiliary electrode 61and the period in which the voltage Vs is applied to the auxiliaryelectrode 61 are provided in each frame. The sensitivity in the periodduring which the voltage V0 is applied to the auxiliary electrode 61 islower than the sensitivity in the period during which the voltage Vs isapplied to the auxiliary electrode 61. However, the sensitivity of theimaging device may not be sufficiently decreased only by the adjustmentof the sensitivity adjustment voltage.

In the example illustrated in FIG. 11, the voltage applied to the upperelectrode 52 is changed via photoelectric converter control line 16 (seeFIG. 1) according to the change in the sensitivity adjustment voltage.Specifically, a predetermined voltage Vp is applied to the upperelectrode 52 in the period (the effective exposure period) during whichthe voltage Vs is applied to the auxiliary electrode 61, and voltage Vqlower than the voltage Vp is applied to the upper electrode 52 in theperiod during which the voltage V0 is applied to the auxiliary electrode61. Like this, the potential of the upper electrode 52 is reduced in theperiods other than the effective exposure period, and thus thesensitivity of the imaging device 101 may be further decreased. Anelectronic shutter operation may be performed more effectively byadjusting the voltage of the upper electrode 52 in addition to thesensitivity adjustment voltage. The voltage applied to the upperelectrode 52 may be supplied via the photoelectric converter controlline 16 from the voltage application circuit 60 or the vertical scanningcircuit 15.

Second Embodiment

Next, an imaging device according to the present embodiment will bedescribed with reference to FIGS. 12A to 13B.

The imaging device of the present embodiment differs from the imagingdevice of the first embodiment in that the auxiliary electrodes areelectrically separated row by row. The configuration of components otherthan the auxiliary electrode and the voltage application circuit may bethe same as that of the first embodiment, and thus the auxiliaryelectrode and the voltage application circuit will be mainly described.

FIG. 12A schematically illustrates an example of planar structure of anauxiliary electrode of the present embodiment. The imaging device of thepresent embodiment includes auxiliary electrode rows 61 ₁, 61 ₂, . . . ,61 _(n) for which the auxiliary electrodes 61 of the unit pixel cells 14within each row are electrically connected. The auxiliary electrode rows61 ₁, 61 ₂, . . . , 61 _(n) are electrically separated from one another.

As illustrated, the auxiliary electrode rows 61 ₁, 61 ₂, . . . , 61 _(n)each have a connection to the voltage application circuit 60A. Thevoltage application circuit 60A is configured to supply at least twosensitivity adjustment voltages to each of the auxiliary electrode rows61 ₁, 61 ₂, . . . , 61 _(n) individually. In the following exampledescribed with reference to FIG. 12A, switching between the twosensitivity adjustment voltages is performed at different times for eachauxiliary electrode row.

FIG. 12B is an example of a timing chart illustrating the timing ofapplication of the sensitivity adjustment voltage, exposure and signalreading in the configuration illustrated in FIG. 12A. In FIG. 12B, SSV1,SSV2, . . . , SSVn illustrate the timing of the change in thesensitivity adjustment voltage applied to the auxiliary electrode rows61 ₁, 61 ₂, . . . , 61 _(n), respectively.

The imaging device of the present embodiment can change the sensitivityadjustment voltage applied to each row of the pixel array at mutuallydifferent timing. Therefore, as illustrated in FIG. 12B, the sensitivityadjustment voltage is changeable in each row of the pixel arrayaccording to a time at which the reset gate voltage is switched from ahigh level to a low level, for instance. Thus, the sensitivityadjustment voltage in each frame may be made nearly constant in each rowof the pixel. That is, the sensitivity is changeable per unit of framein each row.

With the imaging device of the present embodiment, change in thesensitivity adjustment voltage in the middle of an exposure period isavoidable, and thus proper image pickup is performed in every frames.Consequently, continuous frame shooting is possible and the sensitivityis adjustable per unit of frame. For instance, in the imaging device ofthe present embodiment, the sensitivity is adjustable per unit of frame,and thus even in a shooting environment in which brightness changesrapidly, the sensitivity is adjustable by coping with change ofbrightness quickly.

The imaging device of the present embodiment is also applicable to adrive method of adjusting an exposure time by an electronic shutter. Forinstance, as illustrated in FIG. 12C, the period during which the resetgate voltage is set to a high level is provided twice in one frameperiod in each row of the pixel array. Thus, it is possible to divideone frame period into non-exposure time and exposure time. The exposuretime is changeable by changing the time at which the reset gate voltageis set to a high level again in one frame period.

When control of exposure time is applied using such an electronicshutter, it is sufficient that the sensitivity adjustment voltage bechanged in a non-exposure time as illustrated in FIG. 12C. Thus, thesensitivity adjustment voltage is not changed in the middle of anexposure period in each row, and nearly constant sensitivity adjustmentvoltage may be applied over the entire exposure periods. Therefore, animaging device that allows proper image pickup in every frames, enablescontinuous frame shooting, and is capable of adjusting the sensitivityper unit of frame is achieved. Also, it is possible to adjust theexposure time by an electronic shutter.

In the example described with reference to FIGS. 12A to 12C, theauxiliary electrodes of the unit pixel cells 14 in each row areelectrically connected to one another and constitute the auxiliaryelectrode rows. The auxiliary electrode rows are electrically separatedfrom one another. However, the auxiliary electrodes may form groups eachof which includes n rows (n is an integer greater than or equal to 2)rather than 1 row. The auxiliary electrodes in each group may beelectrically connected to one another and the groups may be electricallyseparated from one another.

FIG. 13A schematically illustrates a planar structure of pixelelectrodes in which 2 rows of the pixel array form one group. In theconfiguration illustrated in FIG. 13A, for instance, the auxiliaryelectrodes of the unit pixel cell 14 included in the 1st row of thepixel array and the auxiliary electrodes of the unit pixel cell 14included in the 2nd row of the pixel array form one group. Asillustrated, the auxiliary electrodes belonging to the group areintegrally formed, and thus electrically connected to one another. Inthe configuration illustrated in FIG. 13A, it may be stated that theauxiliary electrodes include a structure in which the auxiliaryelectrode row 61 ₁ and the auxiliary electrode row 61 ₂ illustrated inFIG. 12A are integrally formed.

As illustrated, each of the groups that each include 2 rows of the pixelarray is connected to voltage application circuit 60B. The voltageapplication circuit 60B is configured to supply at least two sensitivityadjustment voltages to each group individually.

FIG. 13B illustrates an example of a timing chart for changing thesensitivity adjustment voltage in the imaging device having theelectrode structure illustrated in FIG. 13A. FIG. 13B illustrates thetiming of application of the sensitivity adjustment voltage, exposureand signal reading. In this example, switching between sensitivityadjustment voltages is performed every 2 rows. As illustrated in FIG.13B, the timing of change in sensitivity adjustment voltage in each ofthe sets SSV1 and SSV2, and SSV3 and SSV4, etc. is common. Also, as seenwith reference to the change in the set of RST1 and RST2, the set ofRST3 and RST4, etc., the reset gate voltage is also switched every 2rows. Therefore, the electronic shutter is also controlled every 2 rows.

It is to be noted that in FIG. 13B, changes in the voltages such as SSV1and SSV2 of the auxiliary electrode rows corresponding to 2 rows of thepixel array are separately illustrated, and in this example, 2 auxiliaryelectrode rows form one group and the auxiliary electrodes 61 in eachgroup are electrically connected to one another. Therefore, practically,SSV1 and SSV2 may have a common signal. Reset gate voltage signals suchas RST1 and RST2 may be common, that are supplied to the unit pixelcells 14 corresponding to the auxiliary electrode rows belonging to thesame group.

In the imaging device in this configuration, n rows as a unit may have acommon change in the sensitivity adjustment voltage to be supplied tothe pixel array. Therefore, the number of signals for adjusting thesensitivity may be reduced to 1/n the number of rows. Consequently, itis possible to reduce the size of the voltage application circuit 60B,simplify the circuit, and decrease the number of wired lines for drivingthe auxiliary electrode 61.

Third Embodiment

An imaging device according to the present embodiment will be describedwith reference to FIG. 14A.

The imaging device of the present embodiment differs from the imagingdevice of the first embodiment in that a light quantity detectioncircuit is further included. The configuration of components other thanthe light quantity detection circuit may be the same as that of thefirst embodiment. The light quantity detection circuit will be mainlydescribed.

FIG. 14A schematically illustrates an example of a circuit configurationof an imaging device 103 according to the present embodiment. Theimaging device 103 further includes a light quantity detection circuit70 in addition to the components of the imaging device 101 of the firstembodiment. The light quantity detection circuit 70 includes a lightdetection device and detects a quantity of light per unit area, which isincident to the photoelectric converter 10. The quantity of light perunit area may be illumination.

The light quantity detection circuit 70 outputs a detection signalregarding the quantity of light per unit area to the voltage applicationcircuit 60C. The voltage application circuit 60C applies a sensitivityadjustment voltage according to the detection signal to the auxiliaryelectrode 61 of each unit pixel cell 14. In the present embodiment, ahole is assumed to serve as a signal charge. For instance, when a largequantity of light is incident to the photoelectric conversion layer perunit area and a detection signal is high, the voltage applicationcircuit 60C supplies a relatively low sensitivity adjustment voltage tothe unit pixel cell 14. Application of a relatively low voltage to theauxiliary electrode 61 causes the sensitivity of the imaging device 103to decrease as described in the first embodiment. Therefore, a highquality image in which overexposed white areas are reduced may beobtained.

Also, when a small quantity of light is incident to the photoelectricconversion layer per unit area and a detection signal is low, thevoltage application circuit 60C supplies a relatively high sensitivityadjustment voltage to the unit pixel cell 14. Application of arelatively high voltage to the auxiliary electrode 61 causes thesensitivity of the imaging device 103 to increase. Therefore, a highquality image in which underexposed black areas are reduced may beobtained.

In this manner, with the imaging device of the present embodiment, thesensitivity is automatically adjusted and image pickup may be performedwith an appropriate sensitivity according to the ambient brightness.

Modification of Third Embodiment

FIG. 14B illustrates another example of a configuration of an imagingdevice according to a third embodiment. The imaging device 103Aillustrated in FIG. 14B has a flash 72. As described with reference toFIG. 10 in the configuration illustrated in FIG. 14B, an operation maybe performed such that the sensitivity of the imaging device 103A istemporarily reduced in synchronization with the timing of firing of theflash. For instance, the voltage application circuit 60C may supply asensitivity adjustment voltage to the unit pixel cell 14, thesensitivity adjustment voltage causing the sensitivity of the imagingdevice 103A to temporarily reduce in synchronization with the timing offiring of the flash.

FIG. 15 illustrates still another example of a configuration of theimaging device according to the third embodiment. The imaging device103B illustrated in FIG. 15 has an input interface 74. In theconfiguration illustrated to FIG. 15, the input interface 74 receives aninput from a user. Here, the input interface 74 is configured to receiveat least input of F value from a user. The example of the inputinterface 74 includes a button, a dial, and a touch screen.

According to the embodiments of the present disclosure, as alreadydescribed with reference to FIG. 4B and FIG. 4D, change in thesensitivity adjustment voltage applied to the auxiliary electrode 61makes it possible to change the size of the region (for instance, seethe region 51A illustrated in FIG. 4B and the region 51C illustrated inFIG. 4D) where signal charges are trapped by the pixel electrode 50.That is, the size of the region that contributes to generation of signalcharges may be changed in each unit pixel cell 14 according to the valueof the sensitivity adjustment voltage. As seen from the comparisonbetween FIG. 4B and FIG. 4D, the region 51A illustrated in FIG. 4B issmaller than the region 51C illustrated in FIG. 4D, and the outerperiphery of the region 51A is located inside the outer periphery of theregion 51C. As illustrated in FIG. 4B, the region (for instance, theregion 51A) which is formed in the photoelectric conversion layer and inwhich signal charges are trapped by the pixel electrode 50 is relativelysmall, and therefore in a state where the sensitivity of the imagingdevice is adjusted to be low, the incident light to a position away fromthe center of the unit pixel cell 14 does not contribute to formation ofan image. That is, a state where the region where signal charges aretrapped by the pixel electrode 50 is reduced corresponds to a statewhere the F value of the camera is increased. This indicates that the Fvalue is controllable by changing the size of the region 51A wheresignal charges are trapped by the pixel electrode 50, using thesensitivity adjustment voltage.

FIG. 15 is referred. In the configuration illustrated to FIG. 15, thevoltage application circuit 60D supplies a sensitivity adjustmentvoltage to the pixel array according to an input from the inputinterface 74. For instance, when a first value as the F value isspecified via the input interface 74, the voltage application circuit60D applies a first sensitivity adjustment voltage (for instance, −2 V)to the auxiliary electrode 61. When a second value smaller than thefirst value as the F value is specified via the input interface 74, thevoltage application circuit 60D applies a second sensitivity adjustmentvoltage (for instance, 5 V) to the auxiliary electrode 61. Applicationof the second sensitivity adjustment voltage to the auxiliary electrode61 causes the region where signal charges are trapped by the pixelelectrode 50 to be increased compared with the case where the firstsensitivity adjustment voltage is applied to the auxiliary electrode 61.The increase of the region where signal charges are trapped by the pixelelectrode 50 achieves a state similar to a state where the F value ofthe camera is reduced.

In this manner, according to the embodiment of the present disclosure,the F value is controllable by adjusting the sensitivity adjustmentvoltage. For the control of the F value using the sensitivity adjustmentvoltage, no diaphragm mechanism needs to be provided, and thus it isalso possible to change the F value continuously. It is to be noted thatin this example, the F value is controlled by changing the sensitivityadjustment voltage based on an operation of the input interface 74 by auser. However, the control of the F value is not limited to theabove-described example. For instance, control of the F value may beperformed automatically by determining the value of the sensitivityadjustment voltage based on the result of detection by the lightquantity detection circuit.

FIG. 16 illustrates an example of disposition of pixel electrodes andauxiliary electrodes in the imaging device having the input interface74.

FIG. 16 illustrates nine unit pixel cells selected from the unit pixelcells in the pixel array. The pixel electrode 50B in each of the unitpixel cells 14B illustrated in FIG. 16 includes nine sub-pixelelectrodes 50 a to 50 i. The sub-pixel electrodes 50 a to 50 i areconnected to the gate electrode 39B (see FIG. 2) of the sameamplification transistor 11 and thus are electrically connected to oneanother. That is, at the time of an operation of the imaging device, thepotentials of the sub-pixel electrodes 50 a to 50 i in a unit pixel cell14B are the same. It is to be noted that in the imaging device of thepresent disclosure, a unit pixel cell to which a pixel electrode ofinterest belongs is determined by an amplification transistor having thegate electrode to which the pixel electrode is connected. That is, whena pixel electrode is connected to the gate electrode of a firstamplification transistor and anther pixel electrode is connected to thegate electrode of a second amplification transistor, these two pixelelectrodes are distinguished as electrodes belonging to different unitpixel cells.

In this example, the sub-pixel electrodes 50 a to 50 i are spatiallyseparately disposed, and the auxiliary electrode 61B encloses each ofthe sub-pixel electrodes 50 a to 50 i. In this example, the auxiliaryelectrodes 61B are electrically connected to one another between theunit pixel cells 14B. Needless to say, the number, shape, anddisposition of the sub-pixel electrodes in the unit pixel cell 14B arenot limited to the example illustrated in FIG. 16. The shape of theauxiliary electrode 61B is not limited to the example illustrated inFIG. 16, either.

As described above, according to the embodiment of the presentdisclosure, change in the sensitivity adjustment voltage makes itpossible to change the size of the region which is in the photoelectricconversion layer 51 and in which signal charges are trapped by the pixelelectrode 50. The sensitivity of the imaging device changes as the sizeof the region where signal charges are trapped by the pixel electrode 50is changed. That is, it is possible to control the sensitivity of theimaging device using the sensitivity adjustment voltage.

However, when the size of the region where signal charges are trapped bythe pixel electrode 50 is extremely changed in accordance with a changein the sensitivity adjustment voltage, the change in the size of theregion may cause an unintended change of the F value. This is becausethe change in the size of the region which is in the photoelectricconversion layer 51 and in which signal charges are trapped by the pixelelectrode 50 causes an effect similar to an effect caused by changingthe size of the diaphragm in the camera.

In the configuration illustrated in FIG. 16, the sub-pixel electrodes 50a to 50 i, which are spatially separated by the auxiliary electrode 61B,are provided within the unit pixel cell 14B. Thus, it is possible toform mutually separated sub-regions in a single unit pixel cell 14Bcorrespondingly to the sub-pixel electrodes 50 a to 50 i. Thesesub-regions are regions where signal charges are trapped by thesub-pixel electrodes 50 a to 50 i. When the sensitivity adjustmentvoltage is changed, the size of each of the sub regions formed in theunit pixel cell 14B is changed. Therefore, the sensitivity of theimaging device changes in accordance with the change in the sensitivityadjustment voltage.

At this point, the change in the size of each of the sub-regions inaccordance with the change in the sensitivity adjustment voltage is ingeneral smaller than the change in the size of the region (for instance,see the region 51A illustrated in FIG. 4B) where signal charges aretrapped by the pixel electrode 50 in the configuration in which the unitpixel cell 14 is provided with a single pixel electrode. That is,formation of sub-regions in each unit pixel cell 14B reduces the rangeof the change in the size of each of the sub-regions while achieving aneffect of sensitivity adjustment due to the change in the sensitivityadjustment voltage. Therefore, it is possible to suppress unintendedchange in the F value while maintaining the effect of the sensitivityadjustment due to the change in the sensitivity adjustment voltage.

It is to be noted that it is also possible to reduce the range of changein the size of the region where signal charges are trapped by the pixelelectrode 50 by decreasing the distance L1 (for instance, see FIG. 3)between the pixel electrode 50 and the auxiliary electrode 61 withoutdividing the pixel electrodes 50 in each unit pixel cell 14. However, itis difficult to sufficiently ensure the range of change in the size ofthe region where signal charges are trapped by the pixel electrode 50 bysimply decreasing the distance L1 in each unit pixel cell 14, and thussufficient sensitivity adjustment effect is not likely to be obtained.

Fourth Embodiment

An imaging device according to the present embodiment will be describedwith reference to FIG. 17.

The imaging device of the present embodiment differs from the imagingdevice of the first embodiment in that an image processing circuit isfurther included. Also, the voltage application circuit supplies two ormore different sensitivity adjustment voltages to the pixel array. Theconfiguration of components other than the image processing circuit andthe voltage application circuit may be the same as that of the firstembodiment. These circuits will be mainly described.

FIG. 17 schematically illustrates an example of a circuit configurationof the imaging device according to the present embodiment. The imagingdevice 104 further includes an image processing circuit 71 in additionto the components of the imaging device 101 of the first embodiment. Theimaging device 104 of the present embodiment picks up the same scenemultiple times with different sensitivities and synthesizes images withdifferent sensitivities. By combining the images obtained with differentsensitivities, an image of a scene having a large contrast ratio withoutoverexposed white area or underexposed black area is generated. Such ashooting method is called high dynamic range imaging.

In the present embodiment, the voltage application circuit 60successively supplies two or more sensitivity adjustment voltages toeach unit pixel cell 14, the two or more sensitivity adjustment voltageshaving a relationship of Vd1>Vd2> . . . >Vdm (m is an integer greaterthan or equal to 2), for instance.

For each of the sensitivity adjustment voltages of Vd1, Vd2, . . . ,Vdm, the imaging device 104 picks up an image with the sensitivityadjustment voltage applied. Image signals G1, G2, . . . , Gm obtained bythe pick-up are outputted from the horizontal signal read circuit 20 tothe image processing circuit 71. For instance, for a frame, imagepick-up is performed with V1 applied as the sensitivity adjustmentvoltage, and for the subsequent frame, image pick-up is performed withone selected from Vd2 to Vdm applied as the sensitivity adjustmentvoltage.

For instance, when a hole serves as a signal charge, in a range in whichthe sensitivity adjustment voltage is lower than the voltage of theupper electrode, the higher the sensitivity adjustment voltage is, thehigher the sensitivity of the imaging device 104 is, and the lower thesensitivity adjustment voltage is, the lower the sensitivity of theimaging device 104 is. For this reason, at least a signal of an imagehaving a relatively low sensitivity and less overexposed white area anda signal of an image having a relatively high sensitivity and lessunderexposed black area are outputted to the image processing circuit71. For instance, the image processing circuit 71 synthesizes these twoimages and generates and outputs a synthetic image. A method forcombining two or more images with different sensitivities is not limitedto a specific method, and various signal processing methods used forhigh dynamic range imaging may be applicable.

Even in a portion having a high luminance or a portion having a lowluminance in an obtained synthetic image, occurrence of overexposedwhite area or underexposed black area is suppressed. Thus, with theimaging device of the present embodiment, it is possible to expand thedynamic range of the imaging device.

Modification of Fourth Embodiment

FIG. 18 illustrates an another example of disposition of pixelelectrodes and auxiliary electrodes in the imaging device according tothe fourth embodiment. FIG. 18 illustrates nine unit pixel cellsselected from the unit pixel cells in the pixel array. As describedbelow, unit pixel cells having different functions may be provided inthe pixel array in a mixed manner.

In the configuration illustrated in FIG. 18, unit pixel cell 14Cincluding pixel electrode 50C and unit pixel cell 14D including pixelelectrode 50D having a smaller area than the pixel electrode 50C arealternately disposed in every other row. In FIG. 18, the unit pixelcells 14C are disposed in odd rows of the pixel array, and the unitpixel cells 14D are disposed in even rows of the pixel array. Asillustrated, in the rows (here, odd rows) in which the unit pixel cells14C are disposed and in the rows (here, even rows) in which the unitpixel cells 14D are disposed, there are provided auxiliary electroderows 61 _(C) each formed so as to surround the pixel electrode 50C andauxiliary electrode rows 61 _(D) each formed so as to surround the pixelelectrode 50D.

A space is formed between the pixel electrode 50C and the auxiliaryelectrode row 61 _(C) of each unit pixel cell 14C. The size of thespace, that is, the distance between the pixel electrode 50C and theauxiliary electrode row 61 _(C) is Lc. A space is also formed betweenthe pixel electrode 50D and the auxiliary electrode row 61 _(D) of eachunit pixel cell 14D. The size of the space, that is, the distancebetween the pixel electrode 50D and the auxiliary electrode row 61 _(D)is Ld. As schematically illustrated in FIG. 18, the distance Ld isgreater than the distance Lc here. Therefore, for instance, even whenthe same sensitivity adjustment voltage is applied to the auxiliaryelectrode row 61 _(C) and the auxiliary electrode row 61 _(D), the sizeof the region where signal charges are trapped by the pixel electrode50C formed in the unit pixel cell 14C is different from the size of theregion where signal charges are trapped by the pixel electrode 50Dformed in the unit pixel cell 14D. That is, in this example, even when acommon sensitivity adjustment voltage is applied, the size of the regionwhere signal charges are trapped by each pixel electrode are differentbetween odd rows and even rows. In other words, in photosensitiveregions, the sensitivity of the unit pixel cell 14C and the sensitivityof the unit pixel cell 14D are different from each other.

In the imaging device having such an electrode structure, an image of anobject is picked up, for instance, with the same sensitivity adjustmentvoltage applied to the auxiliary electrode row 61 _(C) and the auxiliaryelectrode row 61 _(D). After the image pickup, for instance, the imageprocessing circuit 71 (see FIG. 17) forms the image of the object basedon the output from each unit pixel cell.

In this process, the image processing circuit 71 is able to form a firstimage using an image signal outputted from the unit pixel cell 14C aswell as a second image using an image signal outputted from the unitpixel cell 14D. In this example, even when the same sensitivityadjustment voltage is applied to the auxiliary electrode row 61 _(C) andthe auxiliary electrode row 61 _(D), the size of the region where signalcharges are trapped by the pixel electrode 50C formed in the unit pixelcell 14C is different from the size of the region where signal chargesare trapped by the pixel electrode 50D formed in the unit pixel cell14D. Therefore, the first image and second image are images that areobtained with different sensitivities. That is, pixels having differentsizes of the space between the pixel electrode and the auxiliaryelectrode (here, auxiliary electrode row) are provided in the pixelarray in a mixed manner, and thereby an image picked up with differentsensitivities is obtainable at a time.

In this manner, with the configuration illustrated in FIG. 18, an imagepicked up with different sensitivities is obtainable at a time.Therefore, it is possible to perform high dynamic range imaging at ahigh speed, for instance.

The auxiliary electrode row 61 _(C) and the auxiliary electrode row 61_(D) may be electrically separated from each other by being disposed ina spatially separated manner as illustrated in FIG. 18. Alternatively,the auxiliary electrode row 61 _(C) and the auxiliary electrode row 61_(D) may be electrically connected to each other by being integrallyformed. The auxiliary electrode row 61 _(C) and the auxiliary electroderow 61 _(D) may be electrically separated from each other, and therebydifferent sensitivity adjustment voltages may be independently appliedto the auxiliary electrode row 61 _(C) and the auxiliary electrode row61 _(D). When the auxiliary electrode row 61 _(C) and the auxiliaryelectrode row 61 _(D) are integrally formed, the number of wired linesbetween the voltage application circuit 60 and the pixel array may bereduced.

In the configuration illustrated in FIG. 18, the auxiliary electrodesare separated row by row. However, the configuration of the auxiliaryelectrodes is not limited to this example, and the auxiliary electrodesmay be separated for each unit pixel cell, for instance.

FIG. 19 illustrates another example of disposition of the pixelelectrodes and auxiliary electrodes in the imaging device according tothe fourth embodiment. In the configuration illustrated in FIG. 19, eachof the unit pixel cells 14E includes the pixel electrode 50 andauxiliary electrode 61E. In the example illustrated in FIG. 19, thedistance between the pixel electrode 50 and the auxiliary electrode 61Eis the same between nine unit pixel cells 14E illustrated in FIG. 19.

As illustrated, in this example, a space is provide between adjacentunit pixel cells 14E, and thereby the auxiliary electrode 61E iselectrically separated from other auxiliary electrodes 61E in the pixelarray. In such a configuration, it is possible to independently applydifferent sensitivity adjustment voltages to each of the auxiliaryelectrodes 61E in the pixel array. Independent application of differentsensitivity adjustment voltages to each of the auxiliary electrodes 61Ein the pixel array enables adjustment of sensitivity according to anypattern in the pixel array.

FIG. 20 illustrates an example of electrical connection between the unitpixel cell 14E including the pixel electrode 50 and the auxiliaryelectrode 61E, and the voltage application circuit 60. The imagingdevice 104E illustrated in FIG. 20 has sensitivity adjustment line 28corresponding to each unit pixel cell 14E in each row of the pixelarray. Specifically, the auxiliary electrode 61E of each unit pixel cell14E and the voltage application circuit 60 are connected by differentsensitivity adjustment lines 28. The connection between the auxiliaryelectrode 61E and the voltage application circuit 60 by differentsensitivity adjustment lines 28 allows different sensitivity adjustmentvoltages to be applied independently to each auxiliary electrode 61E. Itis to be noted that when a common sensitivity adjustment voltage issupplied to the unit pixel cells 14E belonging to the same row anddifferent sensitivity adjustment voltages are respectively applied tothe odd rows and the even rows of the pixel array, it is also possibleto perform an operation similar to the operation described withreference to FIG. 18. FIG. 21 schematically illustrates an example of across-section of the unit pixel cell 14E.

FIG. 21 corresponds to the sectional view taken along line XXI-XXIillustrated in FIG. 19 and schematically illustrates 3 unit pixel cellsarranged in a row direction.

In the configuration illustrated in FIG. 21, the unit pixel cell 14Ebillustrated in the center of FIG. 21 has a color filter 75 b on theopposite side of the photoelectric conversion layer 51 with respect tothe upper electrode 52. Here, the color filter 75 b is a filter thatallows blue light to pass through. As illustrated, unit pixel cells 14Egare disposed on right side and left side of unit pixel cell 14Eb. Eachof these two unit pixel cells 14Eg has a color filter 75 g on theopposite side of the photoelectric conversion layer 51 with respect tothe upper electrode 52. Here, the color filter 75 g is a filter thatallows green light to pass through. As illustrated, a micro lens 76 maybe disposed on the color filter (here, the color filters 75 b and 75 g).

Each of the unit pixel cell 14Eb and the unit pixel cells 14Egillustrated in FIG. 21 has the pixel electrode 50 and the auxiliaryelectrode 61E. Therefore, the voltage application circuit 60 (see FIG.20) is capable of applying different sensitivity adjustment voltages tothe auxiliary electrodes 61E of the unit pixel cells individually. Here,the voltage application circuit 60 supplies different sensitivityadjustment voltages to the auxiliary electrodes 61E of the unit pixelcells according to the color of light that passes through each colorfilter. For instance, the voltage application circuit 60 applies thefirst voltage as the sensitivity adjustment voltage to the auxiliaryelectrode 61E of B pixel that has the color filter 75 b, and applies thesecond voltage different from the first voltage as the sensitivityadjustment voltage to the auxiliary electrode 61E of G pixel that hasthe color filter 75 g. Also, the voltage application circuit 60 appliesa third voltage to the auxiliary electrode 61E of R pixel having a colorfilter (not illustrated in FIG. 21) that allows red light to passthrough, the third voltage being different from the first and secondvoltages.

In this manner, different sensitivity adjustment voltages are suppliedto the auxiliary electrodes 61E of each unit pixel cell according to acolor of light that passes through a color filter, for instance, therebymaking it possible to set sensitivities for each color individually.That is, it is possible to adjust white balance of an image to beobtained by adjusting the sensitivity adjustment voltage.

What is to be noted is that the gain of each color in an image dataobtained by image pickup is not adjusted but the sensitivity of eachcolor at the time of image pickup is changed. When a conventionaltechnique is used in which the gain of each color in an image dataobtained by image pickup is adjusted, the levels of noise of each colorare also amplified at different rates accompanied by the change in thegain. In contrast to this, according to the present embodiment, thesensitivity at the time of image pickup may be changed for each colorarbitrarily, and thus it is possible to suppress change of color acrossthe entire image, which is caused by amplification of the noise levelsof each color at different rates. Therefore, according to the presentembodiment, it is possible to achieve white balance more easily inresponse to a difference in environment (for instance, whether themorning or the evening) or a difference between light sources at thetime of image pickup.

Fifth Embodiment

An imaging device according to the present embodiment will be describedwith reference to FIG. 22.

The imaging device of the present embodiment differs from the imagingdevice of the first embodiment in that a memory is further included. Theconfiguration of components other than the memory may be the same asthat of the first embodiment. The memory will be mainly described.

FIG. 22 schematically illustrates an example of a circuit configurationof the imaging device according to the present embodiment. The imagingdevice 105 further includes a memory 78 in addition to the components ofthe imaging device 101 of the first embodiment.

The memory 78 receives information (typically, the value of thesensitivity adjustment voltage) on the sensitivity adjustment voltageapplied to the auxiliary electrode 61, for instance from the voltageapplication circuit 60F at the time of image pickup and stores theinformation temporarily. The information on the sensitivity adjustmentvoltage used at the time of image pickup is associated with an obtainedimage signal, and is read along with an image signal or image data.

The value of the sensitivity adjustment voltage used at the time ofimage pickup is stored in the memory 78, and thus it is possible toprovide the information regarding the scene at the time of image pickuplater after the image pickup. In other words, the information on thesensitivity used for image pickup is available after the image pickup.For instance, based on the value of a sensitivity adjustment voltageassociated with an image, it is possible to distinguish whether theimage is picked up in a dark environment or picked up in a state wherethe sensitivity is decreased by controlling the sensitivity adjustmentvoltage.

The value of the sensitivity adjustment voltage may also be utilized inthe above-described high dynamic range imaging. For instance, the imageprocessing circuit 71 (see FIG. 17) may utilize information on thesensitivity adjustment voltages associated with images which areobtained with changed sensitivities, and may determine the order of thedegree of sensitivity (may be referred to as the magnitude of exposure)at the time of pickup of those images. The image processing circuit 71is capable of combining a plurality of images based on the order of thedegree of the sensitivity at the time of image pickup.

It is to be noted that when image pickup is performed with differentsensitivity adjustment voltages applied to the pixel arraysimultaneously, information regarding how large magnitude of thesensitivity adjustment voltage is applied to which unit pixel cell maybe stored in the memory 78. The memory 78 may be disposed inwardly ofthe imaging device 105 or may be disposed outwardly of the imagingdevice 105. Alternatively, the memory 78 may be detachable from the mainbody of the imaging device 105. As the memory 78, a publicly knownstorage device such as a RAM, a hard disk may be used.

Sixth Embodiment

An imaging device according to the present embodiment will be describedwith reference to FIGS. 23, 24A and 24B.

FIG. 23 illustrates an example of disposition of pixel electrodes andauxiliary electrodes in an imaging device according to a sixthembodiment. In the configuration illustrated in FIG. 23, each of theunit pixel cells 14G includes the pixel electrode 50 and an auxiliaryelectrode 61G disposed so as to surround the pixel electrode 50. Asillustrated, the auxiliary electrode 61G includes sub auxiliaryelectrodes 61 a to 61 d that are spatially separated from one another.Here, the sub auxiliary electrodes 61 a to 61 d are disposed along eachside of the rectangular pixel electrode.

Each of the sub auxiliary electrodes 61 a to 61 d is electricallyconnected to the voltage application circuit 60 (for instance, see FIG.20), thereby being configured to receive application of mutuallyindependent sensitivity adjustment voltages. That is, in this example,at the time of an operation of the imaging device, the potentials of thesub auxiliary electrodes 61 a to 61 d are independently controlled ineach of the unit pixel cells 14G. As described in detail in thefollowing, the sub auxiliary electrodes are disposed in each unit pixelcell, and the voltage in each of the sub auxiliary electrodes iscontrolled, thereby providing the unit pixel cell with a function ofphase difference detection.

FIG. 24A illustrates an example of the region 51A that is formed in thephotoelectric conversion layer 51 of the unit pixel cell 14G. Asdescribed above, the region 51A is a region where signal charges aretrapped by the pixel electrode 50. FIG. 24A corresponds to the sectionalview taken along line XXIVA-XXIVA illustrated in FIG. 23. For the sakeof simplicity, FIG. 24A illustrates a schematic sectional view of thecentral one of nine unit pixel cells illustrated in FIG. 23.

FIG. 24A schematically illustrates the region 51A in a state where thefirst sensitivity adjustment voltage (for instance, −2 V) is applied tothe sub auxiliary electrode 61 a and the second sensitivity adjustmentvoltage (for instance, 5 V) is applied to the sub auxiliary electrode 61d. Here, it is assumed that a common voltage is applied to the subauxiliary electrode 61 b and the sub auxiliary electrode 61 c.

In the state illustrated in FIG. 24A, the potential of the sub auxiliaryelectrode 61 a is lower than the potential of the sub auxiliaryelectrode 61 d, and the sub auxiliary electrode 61 a traps more signalcharges (here, holes) than the sub auxiliary electrode 61 d. That is, asschematically illustrated in FIG. 24A, region 51Ba formed on the subauxiliary electrode 61 a is larger than region 51Bd formed on the subauxiliary electrode 61 d. Therefore, the region 51A at this point is ina shape that is displaced to the right side in FIG. 24A.

FIG. 24B schematically illustrates the region 51A in a state where thesecond sensitivity adjustment voltage is applied to the sub auxiliaryelectrode 61 a and the first sensitivity adjustment voltage is appliedto the sub auxiliary electrode 61 d. In the state which illustrated inFIG. 24B, the region 51Bd formed on the sub auxiliary electrode 61 d islarger than the region 51Ba formed on the sub auxiliary electrode 61 a.Therefore, the region 51A at this point is in a shape that is displacedto the left side in FIG. 24B.

In this manner, the potentials of the sub auxiliary electrodes 61 a and61 d are independently controlled, thereby making it possible to extendthe region 51A toward the sub auxiliary electrode 61 a or toward the subauxiliary electrode 61 d in the photoelectric conversion layer 51.Similarly, the potentials of the sub auxiliary electrodes 61 b and 61 care adjusted with a common potential applied to the sub auxiliaryelectrodes 61 a and 61 d, thereby making it possible to extend theregion 51A upward or downward in FIG. 23. Also, for instance, when thefirst sensitivity adjustment voltage is applied to the sub auxiliaryelectrodes 61 a and 61 b and the second sensitivity adjustment voltageis applied to the sub auxiliary electrodes 61 c and 61 d, it is possibleto extend the region 51A to the upper right direction in FIG. 23. Inthis manner, the potentials of the sub auxiliary electrodes 61 a to 61 dare independently controlled, thereby making it possible to extend theregion 51A to any direction in the photoelectric conversion layer 51.

For instance, when the region 51A in a pixel in the pixel array isextended to the right side as illustrated in FIG. 24A, and the region51A in the adjacent pixel to the left side of the pixel is extended tothe left side as illustrated in FIG. 24B, the set of those pixels may beutilized as pixels for phase difference auto focus (AF). Needless tosay, when a common sensitivity adjustment voltage is applied to the foursub auxiliary electrodes 61 a to 61 d, the unit pixel cell 14G iscapable of functioning similarly to the other embodiments describedabove.

As is apparent from FIG. 24A and FIG. 24B, the device structures of theunit pixel cell for image pickup and the unit pixel cell for phasedifference AF are common in the present embodiment. Therefore, the phasedifference AF is achieved without disposing a pixel for phase differenceAF separately in the pixel array or disposing a sensor for phasedifference AF separately in the imaging device. According to the presentembodiment, control of the sensitivity adjustment voltage applied to thesub auxiliary electrodes enables any unit pixel cell in the pixel arrayto function as a pixel for phase difference AF, and thus more flexibleapplication is possible.

It is to be noted that the number, shape, and disposition of the subauxiliary electrodes in the unit pixel cell are not limited to theexample illustrated in FIG. 23, and may be set in any manner. In thepresent embodiment, it may be stated that the “unit pixel cell” is aminimum unit that constitutes a repeated structure of a photosensitiveregion and includes at least one pixel electrode.

Seventh Embodiment

An image acquisition device according to the present embodiment will bedescribed with reference to FIGS. 25A to 30.

The image acquisition device according to the present embodiment detectslight beam that passes through an object. The object is disposed closeto a photoelectric converter of the imaging device. The imageacquisition device provides different directions of irradiation of lightbeam that passes through an object, thereby allowing the same pixel todetect light beams that pass through different portions of the object.Obtained image signals are synthesized and thus an image with a highresolution is obtained.

FIG. 25A schematically illustrates the configuration of an imageacquisition device according to a seventh embodiment of the presentdisclosure. An image acquisition device 106 illustrated in FIG. 25A hasan illumination system 81, an imaging device 100, and an image processor90.

The imaging device in any one of the first to sixth embodiments may beused as the imaging device 100. In the present embodiment, the imagingdevice 101 of the first embodiment is used, for instance. FIG. 25Bschematically illustrates an example of a configuration of theillumination system 81. The illumination system 81 includes lightsources 81 a to 81 i that are arranged two-dimensionally, for instance.

FIG. 26A schematically illustrates the configuration of the illuminationsystem 81 and the vicinity of the photoelectric converter 10 of theimaging device 101. As illustrated in FIG. 26A, an object 80 is disposedaway from the upper electrode 52 of the photoelectric converter 10 bydistance L2, for instance. The distance L2 is typically 1 mm or lessand, for instance, approximately 0.1 μm or more and approximately 10 μmor less. The object 80 is disposed in parallel to the photoelectricconverter 10. The imaging device 101 may include an arrangement surfacefor holding the object 80. Here, a light condensing optical element suchas a micro lens is not disposed on the upper electrode 52 of thephotoelectric converter 10. The object 80 is, for instance, an opticallytransparent sample (such as a cell, a sliced tissue) held on a preparedslide.

The illumination system 81 is disposed at a position sufficientlydistant from the photoelectric converter 10. In FIG. 26A, three lightsources 81 a to 81 c out of the light sources 81 a to 81 i areillustrated. The light source 81 a out of the light sources 81 a, 81 b,81 c is disposed in the central vicinity of the two-dimensionallydisposed unit pixel cells 14 of the imaging device 101. On the otherhand, the light sources 81 b, 81 c are disposed away from the centralvicinity. Although the light sources 81 a, 81 b, 81 c are each typicallya point light source, the light sources 81 a, 81 b, 81 c aresufficiently away from the photoelectric converter 10. Thus the lightsources 81 a, 81 b, 81 c irradiate the object 80 with illumination lightwhich is parallel light. As illustrated in FIG. 26A, the light source 81a irradiates the object 80 over the photoelectric converter 10 withillumination light in a vertical direction. On the other hand, asillustrated in FIG. 26B, the light source 81 b irradiates the object 80with illumination light in a direction inclined to the normal directionto the object 80. The same goes for the light source 81 c. In thismanner, the illumination system 81 successively emits illumination lightin different directions of irradiation with respect to the object 80 asa reference, and irradiates the object 80 with illumination light.

Next, the step for the image acquisition device 106 to obtain the imageof the object 80 will be described.

First, a predetermined sensitivity adjustment voltage Vk is applied tothe auxiliary electrode 61. As described in the first embodiment, byapplying the sensitivity adjustment voltage to the auxiliary electrode61, the signal charges generated in region 51B including the overlappingportion with the auxiliary electrode 61 in a plan view within thephotoelectric conversion layer 51 move to the auxiliary electrode 61.Also, the signal charges generated in region 51A including theoverlapping portion with the pixel electrode 50 in a plan view withinthe photoelectric conversion layer 51 are detected by the pixelelectrode 50. That is, the size of the region 51A specifies a pixelsize.

Next, the light source 81 a is turned on to irradiate the object 80 withillumination light. The illumination light, which passes through theobject 80, enters the photoelectric converter 10. As described above,out of the incident light to the photoelectric converter 10, theincident light to the region 51A where signal charges are trapped by thepixel electrode 50 is essentially detected. That is, region 80A of theobject 80 is selectively picked up, the region 80A being locatedimmediately above the region 51A which is formed in the photoelectricconversion layer 51.

Next, as illustrated in FIG. 26B, the light source 81 b is turned on toirradiate the object 80 with illumination light. The illumination lightfrom the light source 81 b is diagonally incident to the object 80 withrespect to the normal line to the object 80. Therefore, the light, whichpasses through region 80B of the object 80 rather than the region 80A ofthe object 80, is incident to the region 51A, the region 80B beinglocated diagonally above the region 51A, the region 80A being locatedimmediately above the region 51A. As seen from FIG. 26B, illuminationlight, which passes through the region 80A of the object 80, is incidentto the region 51B of the photoelectric conversion layer 51. Therefore,when the light source 81 b is turned on, the region 80B of the object isselectively picked up.

Subsequently, image pickup is performed similarly using light source 81g and light source 81 h of the illumination system 81 illustrated inFIG. 25B. FIG. 27 is a schematic plan view of the object 80 andillustrates the regions 80A, 80B, 80G, 80H that are picked up using thelight sources 81 a, 81 b, 81 g, 81 h. As illustrated in FIG. 26B, theregion 51A of the photoelectric conversion layer 51 is located below theregion 80A. As schematically illustrated by arrows in FIG. 26B, by usingthe light sources 81 b, 81 g, 81 h, the light, which passes through theregions 80B, 80G, and 80H of the object 80, is detectable in the region51A of the photoelectric conversion layer 51. Therefore, all the regionsof the object 80 may be picked up by performing image pickup four timesusing the light sources 81 a, 81 b, 81 g, and 81 h. That is, byperforming image pickup four times while changing an illuminationdirection, the light, which passes through the regions 80A, 80B, 80G,and 80H (see FIG. 27), is successively detectable in the region 51A, theregions 80A, 80B, 80G, and 80H (see FIG. 27) being mutually differentand included in region Px corresponding to one unit pixel cell 14 of theobject 80.

The image processor 90 includes, for instance, one or more processors,and synthesizes image signals obtained by image pickup using the lightsources 81 a, 81 b, 81 g, and 81 h. In this process, the image signalsare rearranged to conform to the arrangement illustrated in FIG. 27.That is, the image processor 90 synthesizes image signals so that theimage signals compensate one another, and generates a synthetic image,thereby forming a high resolution image of the object, which is higherin resolution than an image obtained by performing image pickup one timeusing any one of the light sources 81 a, 81 b, 81 g, and 81 h.

In the image acquisition device 106, the size of the region 51A of thephotoelectric conversion layer 51 determines the resolution of a pickedup image of the object. The smaller the region 51A is, the higher theresolution of a picked up image is. Hereinafter, the step to obtain animage of the object 80 with reduced region 51A will be described withreference to FIGS. 28A to 28C and 29.

First, a predetermined sensitivity adjustment voltage Vh is applied tothe auxiliary electrode 61. When an electron hole serves as a signalcharge, the sensitivity adjustment voltage Vh is set lower than theaforementioned Vk so that the region 51A of the photoelectric conversionlayer 51 becomes small. Consequently, as illustrated in FIG. 28A, theregion 51A of the photoelectric conversion layer 51 becomes smaller thanthe region 51A as illustrated in FIG. 26A and FIG. 26B.

Next, the light source 81 a is turned on to irradiate the object 80 withillumination light. Accordingly, the region 80A of the object 80 ispicked up.

Next, as illustrated in FIG. 28B, the light source 81 b is turned on toirradiate the object 80 with illumination light. The illumination lightfrom the light source 81 b is diagonally incident to the object 80 withrespect to the normal line to the object 80. When the light source 81 bis turned on, the region 80B of the object is picked up.

Next, as illustrated in FIG. 28C, light source 81 c is turned on toirradiate the object 80 with illumination light. Similarly, theillumination light from the light source 81 c is diagonally incident tothe object 80 with respect to the normal line to the object 80. When thelight source 81 c is turned on, the region 80C of the object is pickedup.

Subsequently, image pickup is performed similarly using the lightsources 81 d to 81 i of the illumination system 81 illustrated in FIG.25B. FIG. 29 is a schematic plan view of the object 80 and illustratesthe regions 80A to 80I of the object that are picked up using the lightsources 81 a to 81 i. As schematically illustrated by arrows in FIGS.28B and 28C, by using the light sources 81 b to 81 i, the light, whichpasses through the regions 80B to 80I of the object 80, is detectable inthe region 51A of the photoelectric conversion layer 51. Therefore, allthe regions of the object 80 may be picked up by performing image pickupnine times using the light sources 81 a to 81 i. That is, the light,which passes through different regions, is successively detectable inthe region 51A.

The image processor 90 rearranges and synthesizes image signals toconform to the arrangement illustrated in FIG. 29, the image signalsbeing obtained by image pickup using the light sources 81 a to 81 i,respectively. Consequently, a high resolution image of the object isformed, which is higher in resolution than an image obtained byperforming image pickup one time using any one of the light sources 81 ato 81 i.

It is to be noted that even when the sensitivity adjustment voltage ischanged, the size of the unit pixel cell 14 does not change, and a pixelpitch does not change, either. However, the size of the region 51Acorresponding to the size of effective pixel is changeable. In the imageacquisition device 106, the size of the region 51A determines aresolution. The value of the sensitivity adjustment voltage isdetermined so that the size of the region 51A becomes small, andapplication of the sensitivity adjustment voltage enables a highresolution image to be obtained. For instance, in the exampleillustrated in FIG. 27, adjustment of the size of the region 51A to ¼the size of the unit pixel cell 14 provides an image with a resolution 4times higher than the resolution as in the case where the size of theregion 51A is set to be equivalent to the size of the unit pixel cell14. In the example illustrated in FIG. 29, adjustment of the size of theregion 51A to 1/9 the size of the unit pixel cell 14 provides an imagewith a resolution 9 times higher than the resolution as in the casewhere the size of the region 51A is set to be equivalent to the size ofthe unit pixel cell 14.

In this manner, in the image acquisition device of the presentembodiment, the size of the region 51A where signal charges are trappedby the pixel electrode 50 in the photoelectric conversion layer 51 ischangeable by changing the sensitivity adjustment voltage applied to theauxiliary electrode 61. Therefore, it is possible to change theresolution. It is possible to obtain a high resolution image by reducingthe size of the region 51A.

It is to be noted that in the present embodiment, the illuminationsystem 81 includes a plurality of light sources, and irradiates anobject with illumination light in different directions of irradiationbased on the positions of light sources. However, the illuminationsystem may include one light source, and the orientation of an imagingdevice on which an object is supported may be varied. For instance asillustrated in FIG. 30, the illumination system may include aparallel-light light source 83 and a mechanism 82 that changes theposture of an object. The mechanism 82 may include a goniometer 82A anda rotation mechanism 82B. The goniometer 82A supports the imaging device101 and the object 80. This illumination system allows the posture ofthe object 80 with respect to the parallel-light light source 83 to bevaried. Therefore, the object 80 is able to receive illumination lightfrom the parallel-light light source 83 in different directions withrespect to the object 80 as a reference.

For an imaging device, it is useful to change the size of the region 51Awhere signal charges are trapped by the pixel electrode 50 in thephotoelectric conversion layer 51 by changing the sensitivity adjustmentvoltage applied to the auxiliary electrode 61. That is, since thedistance between the regions 51A of adjacent pixels is increased byreducing the size of the regions 51A, it is possible to suppress colormixing.

The imaging device and the image acquisition device according to thepresent disclosure is useful for an imaging device such as a digitalcamera and an image sensor.

The present disclosure also includes the following aspects.

-   [Item 1]

The imaging device of the above-described embodiment may further includea memory that stores a value of a voltage applied to the auxiliaryelectrode at the time of image pickup.

With this configuration, the value of a sensitivity adjustment voltageused in the image pickup may be saved as information related to imagedata.

-   [Item 2]

In the imaging device of the above-described embodiment, the auxiliaryelectrodes may be separated for each unit pixel cell.

With this configuration, adjustment of sensitivity according to anypattern in the pixel array is possible.

-   [Item 3]

In the imaging device according to Item 2, the unit pixel cells eachinclude a first unit pixel cell having a color filter of a first color,and a second unit pixel cell having a color filter of a second color,and the voltage application circuit may apply different voltages to theauxiliary electrode of the first unit pixel cell and the auxiliaryelectrode of the second unit pixel cell.

With this configuration, it is possible to make white balance adjustmentaccording to a scene.

-   [Item 4]

In the imaging device of the above-described embodiment, the voltageapplication circuit may switch between voltages to be applied to theauxiliary electrode in one frame.

With this configuration, it is possible to synchronize the exposureperiods in all the unit pixel cells included in the pixel array.

-   [Item 5]

In the imaging device according to Item 4, the voltage applicationcircuit may periodically change the voltage to be applied to theauxiliary electrode in one frame.

With this configuration, it is possible to remove the effect of aperiodic flickering of the light that is incident on the imaging device.

-   [Item 6]

The imaging device of the above-described embodiment may further includean illumination device and the voltage application circuit may switchbetween voltages to be applied to the auxiliary electrode according toan operation of the illumination device.

With this configuration, it is possible to remove the effect of locus ofillumination light.

-   [Item 7]

The imaging device according to any one of Items 4 to 6 may furtherinclude a control line that supplies a voltage to the upper electrode,the voltage changings according to switching of the voltage to beapplied to the auxiliary electrode.

With this configuration, by changing the voltage to be applied to theupper electrode according to switching of the voltage to be applied tothe auxiliary electrode, it is possible to set the sensitivity used inthe imaging device to nearly 0. Therefore, the change in the voltage tobe applied to the auxiliary electrode and in the voltage to be appliedto the upper electrode may be utilized as a shutter.

-   [Item 8]

In the imaging device of the above-described embodiment, the voltageapplication circuit may apply a different voltage to the auxiliaryelectrode according to a specified F value.

With this configuration, it is possible to control the F value withoutusing a diaphragm mechanism.

-   [Item 9]

In the imaging device of the above-described embodiment, each of pixelelectrodes is surrounded by the auxiliary electrode and may also includesub-pixel electrodes that are spatially separated.

With this configuration, it is possible to set the sensitivity used inthe imaging device to nearly 0 while maintaining wide incident anglecharacteristics.

-   [Item 10]

In the imaging device of the above-described embodiment, the unit pixelcells may also include a first unit pixel cell in which a first gap isformed between the pixel electrode and the auxiliary electrode, and asecond unit pixel cell in which a second gap larger than the first gapis formed between the pixel electrode and the auxiliary electrode.

With this configuration, it is possible to dispose pixels havingdifferent functions in the pixel array.

-   [Item 11]

In the imaging device of the above-described embodiment, each auxiliaryelectrode may include sub auxiliary electrodes and each of the subauxiliary electrodes may have an electrical connection to the voltageapplication circuit.

With this configuration, it is possible to deform a region, in whichholes movable to the pixel electrode are distributed, into a shape thatis displaced from the center. Therefore, it is possible to utilize eachunit pixel cell for phase difference detection and it is possible toflexibly change the shape of the region in which holes movable to thepixel electrode are distributed, using sensitivity adjustment voltage.

-   [Item 12]

The imaging device of the above-described embodiment may further includean image processing circuit, the voltage application circuit may applydifferent voltages in at least two frames, the image processing circuitmay synthesize the image signals in the at least two frames and mayoutput a synthetic image signal.

With this configuration, it is possible to obtain an image having a highcontrast ratio.

What is claimed is:
 1. An imaging device, comprising: a pixelcomprising: a photoelectric conversion layer having a first surface anda second surface opposite to the first surface; a pixel electrode on thefirst surface; an auxiliary electrode on the first surface, theauxiliary electrode being spaced from the pixel electrode; an upperelectrode on the second surface, the upper electrode facing the pixelelectrode and the auxiliary electrode; and an amplification transistorhaving a gate coupled to the pixel electrode; and voltage applicationcircuitry that generates a first voltage and a second voltage differentfrom the first voltage, the voltage application circuitry being coupledto the auxiliary electrode, wherein the voltage application circuitryselectively supplies either the first voltage or the second voltage tothe auxiliary electrode.
 2. An imaging device according to claim 1,further comprising a line that is coupled between the voltageapplication circuitry and the auxiliary electrode, wherein the voltageapplication circuitry selectively supplies either the first voltage orthe second voltage to the auxiliary electrode via the line.
 3. Theimaging device according to claim 1, further comprising light quantitydetection circuitry that detects a quantity of light per unit area, thelight being incident to the photoelectric conversion layer, wherein thevoltage application circuitry selectively supplies either the firstvoltage or the second voltage to the auxiliary electrode based on thequantity of light per unit area detected by the light quantity detectioncircuitry.
 4. The imaging device according to claim 1, furthercomprising image processing circuitry, wherein the voltage applicationcircuitry supplies the first voltage to the auxiliary electrode in afirst frame period and supplies the second voltage to the auxiliaryelectrode in a second frame period different from the first frameperiod, and the image processing circuitry synthesizes a first imagesignal output from the pixel in the first frame period and a secondimage signal output from the pixel in the second frame period andoutputs a synthetic image signal.
 5. An image acquisition devicecomprising: an illumination system that irradiates an object with eachof beams in sequence, incident directions of the beams with respect tothe object being different from each other; the imaging device accordingto claim 1 located at a position where the beams passing through theobject are inputted, the imaging device acquiring images correspondingto the beams respectively, each of the images having a first resolution;and an image processor that synthesizes the images to generate asynthetic image having a second resolution higher than the firstresolution.
 6. The image acquisition device according to claim 5,wherein the imaging device includes an arrangement surface for holdingthe object, the arrangement surface being located on a side of the upperelectrode opposite to the photoelectric conversion layer.
 7. The imageacquisition device according to claim 5, wherein the image processorsynthesizes the images by interpolating the images with each other. 8.An imaging device, comprising: at least one pixel each comprising: aphotoelectric conversion layer having a first surface and a secondsurface opposite to the first surface; a pixel electrode on the firstsurface; an auxiliary electrode on the first surface, the auxiliaryelectrode being spaced from the pixel electrode; an upper electrode onthe second surface, the upper electrode facing the pixel electrode andthe auxiliary electrode; and an amplification transistor having a gatecoupled to the pixel electrode; and voltage application circuitry thatgenerates a first voltage and a second voltage different from the firstvoltage, the voltage application circuitry being coupled to theauxiliary electrode of one of the at least one pixel, wherein thevoltage application circuitry selectively supplies either the firstvoltage or the second voltage to the auxiliary electrode of the one ofthe at least one pixel.
 9. An imaging device according to claim 8,further comprising a line that is coupled between the voltageapplication circuitry and the auxiliary electrode of the one of the atleast one pixel, wherein the voltage application circuitry selectivelysupplies either the first voltage or the second voltage to the auxiliaryelectrode of the one of the at least one pixel via the line.
 10. Theimaging device according to claim 8, wherein the at least one pixelincludes pixels, and the pixels are arranged one-dimensionally ortwo-dimensionally.
 11. The imaging device according to claim 10, whereinthe auxiliary electrodes of the pixels are coupled to each other. 12.The imaging device according to claim 11, wherein the voltageapplication circuitry switches between the first voltage and the secondvoltage per two frames.
 13. The imaging device according to claim 10,wherein the pixels are arranged two-dimensionally in rows and columns,and the auxiliary electrodes of the pixels belonging to a same row arecoupled to each other.
 14. The imaging device according to claim 13,wherein the pixels form a group for every n contiguous rows when n is aninteger greater than or equal to 2, the auxiliary electrodes of thepixels belonging to a same group are coupled to each other, and theauxiliary electrodes of the pixels belonging to different groups areelectrically separated from each other.
 15. An image acquisition devicecomprising: an illumination system that irradiates an object with eachof beams in sequence, incident directions of the beams with respect tothe object being different from each other; the imaging device accordingto claim 1 located at a position where the beams passing through theobject are inputted, the imaging device acquiring images correspondingto the beams respectively, each of the images having a first resolution;and an image processor that synthesizes the images to generate asynthetic image having a second resolution higher than the firstresolution.
 16. The image acquisition device according to claim 15,wherein the imaging device includes an arrangement surface for holdingthe object, the arrangement surface being located on a side of the upperelectrode opposite to the photoelectric conversion layer.
 17. The imageacquisition device according to claim 15, wherein the image processorsynthesizes the images by interpolating the images with each other.